EP0610055B1 - Zusammengesetzte Objetivlinse mit zwei Brennpunkten, und Vorrichtung mit dieser Linse - Google Patents

Zusammengesetzte Objetivlinse mit zwei Brennpunkten, und Vorrichtung mit dieser Linse Download PDF

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Publication number
EP0610055B1
EP0610055B1 EP94300717A EP94300717A EP0610055B1 EP 0610055 B1 EP0610055 B1 EP 0610055B1 EP 94300717 A EP94300717 A EP 94300717A EP 94300717 A EP94300717 A EP 94300717A EP 0610055 B1 EP0610055 B1 EP 0610055B1
Authority
EP
European Patent Office
Prior art keywords
light
information
hologram
information medium
lens
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
EP94300717A
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English (en)
French (fr)
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EP0610055A3 (de
EP0610055A2 (de
Inventor
Yoshiaki Komma
Sadao Mizuno
Seiji Nishino
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Panasonic Holdings Corp
Original Assignee
Matsushita Electric Industrial Co Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority to EP03020262A priority Critical patent/EP1381034B1/de
Priority to EP97122035A priority patent/EP0836178B1/de
Priority to EP05012296A priority patent/EP1577887A3/de
Priority to EP99123036A priority patent/EP0992988A3/de
Application filed by Matsushita Electric Industrial Co Ltd filed Critical Matsushita Electric Industrial Co Ltd
Priority to EP06021193A priority patent/EP1736976B1/de
Priority to EP03020261A priority patent/EP1376558B1/de
Priority to EP03020259A priority patent/EP1381038B1/de
Priority to EP03020260A priority patent/EP1381039B1/de
Priority to EP00111253A priority patent/EP1049084B8/de
Publication of EP0610055A2 publication Critical patent/EP0610055A2/de
Publication of EP0610055A3 publication Critical patent/EP0610055A3/de
Application granted granted Critical
Publication of EP0610055B1 publication Critical patent/EP0610055B1/de
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
    • G11B7/09—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
    • G11B7/0945—Methods for initialising servos, start-up sequences
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B21/00—Microscopes
    • G02B21/02—Objectives
    • G02B21/025—Objectives with variable magnification
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B21/00—Microscopes
    • G02B21/18—Arrangements with more than one light path, e.g. for comparing two specimens
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B21/00—Microscopes
    • G02B21/18—Arrangements with more than one light path, e.g. for comparing two specimens
    • G02B21/20—Binocular arrangements
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/42—Diffraction optics, i.e. systems including a diffractive element being designed for providing a diffractive effect
    • G02B27/4233—Diffraction optics, i.e. systems including a diffractive element being designed for providing a diffractive effect having a diffractive element [DOE] contributing to a non-imaging application
    • G02B27/4238—Diffraction optics, i.e. systems including a diffractive element being designed for providing a diffractive effect having a diffractive element [DOE] contributing to a non-imaging application in optical recording or readout devices
    • G—PHYSICS
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    • G02B3/10—Bifocal lenses; Multifocal lenses
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    • G02B5/1814—Diffraction gratings structurally combined with one or more further optical elements, e.g. lenses, mirrors, prisms or other diffraction gratings
    • G02B5/1819—Plural gratings positioned on the same surface, e.g. array of gratings
    • G—PHYSICS
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    • G02B5/1871—Transmissive phase gratings
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    • G03F9/70—Registration or positioning of originals, masks, frames, photographic sheets or textured or patterned surfaces, e.g. automatically for microlithography
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    • G11B19/127—Control of operating function, e.g. switching from recording to reproducing by sensing distinguishing features of or on records, e.g. diameter end mark involving detection of the number of sides, e.g. single or double, or layers, e.g. for multiple recording or reproducing layers
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    • G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
    • G11B7/085—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam into, or out of, its operative position or across tracks, otherwise than during the transducing operation, e.g. for adjustment or preliminary positioning or track change or selection
    • G11B7/08505—Methods for track change, selection or preliminary positioning by moving the head
    • G11B7/08511—Methods for track change, selection or preliminary positioning by moving the head with focus pull-in only
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    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
    • G11B7/09—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
    • G11B7/0901—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following for track following only
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
    • G11B7/09—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
    • G11B7/0908—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following for focusing only
    • G11B7/0909—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following for focusing only by astigmatic methods
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    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
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    • G11B7/09—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
    • G11B7/0908—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following for focusing only
    • G11B7/0912—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following for focusing only by push-pull method
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    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
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    • G11B2007/0003—Recording, reproducing or erasing systems characterised by the structure or type of the carrier
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    • G11B7/007—Arrangement of the information on the record carrier, e.g. form of tracks, actual track shape, e.g. wobbled, or cross-section, e.g. v-shaped; Sequential information structures, e.g. sectoring or header formats within a track
    • G11B7/00736—Auxiliary data, e.g. lead-in, lead-out, Power Calibration Area [PCA], Burst Cutting Area [BCA], control information

Definitions

  • the present invention relates to an imaging optical system for converging light on two converging spots, e.g. placed at different depths of an information medium, with a compound objective lens composed of an objective lens and a hologram lens which has two focal points, an optical head apparatus for recording, reproducing or erasing information on or from an information medium such as an optical medium or a magneto-optical medium like an optical disk or an optical card with the imaging optical system and an optical disk apparatus for recording or reproducing information on or from an optical disk with the compound objective lens.
  • an imaging optical system for converging light on two converging spots, e.g. placed at different depths of an information medium, with a compound objective lens composed of an objective lens and a hologram lens which has two focal points
  • an optical head apparatus for recording, reproducing or erasing information on or from an information medium such as an optical medium or a magneto-optical medium like an optical disk or an optical card with the imaging optical system
  • an optical disk apparatus for recording or reproducing information on or from an
  • optical memory technique has been put to practical use to manufacture an optical disk in which a pit pattern formed of a series of pits is drawn to record information.
  • the optical disk is utilized as a high density and large capacity of information medium.
  • the optical disk is utilized for a digital audio disk, a video disk, a document file disk, and a data file disk.
  • a light beam radiated from a light source is minutely converged in an imaging optical system, and the light beam minutely converged is radiated to the optical disk through the imaging optical system. Therefore, the light beam is required to be reliably controlled in the imaging optical system with high accuracy.
  • the imaging optical system is utilized for an optical head apparatus in which a detecting system is additionally provided to detect the intensity of the light beam reflected from the optical disk.
  • Fundamental functions of the optical head apparatus are classified into a converging performance for minutely converging a light beam to form a diffraction-limited micro-spot of the light beam radiated on the optical disk, a focus control in a focus servo system, a tracking control in a tracking serve system, and the detection of pit signals (or information signals) obtained by radiating the light beam on a pit pattern of the optical disk.
  • the fundamental function of the optical head apparatus is determined by the combination of optical sub-systems and a photoelectric transfer detecting process according to a purpose and a use. Specifically, an optical head apparatus in which a holographic optical element (or hologram) is utilized to minimize and thin the optical head apparatus has been recently proposed.
  • Fig. 1 is a constitutional view of a conventional optical head apparatus proposed in Japanese Patent Application No. 46630 of 1991 which is applied by inventors of the present invention.
  • a conventional optical head apparatus 11 for recording or reproducing information on or from an information medium 12 such as an optical disk is provided with a light beam source 13 such as a semiconductor laser, a transmission type of blazed hologram 14 for transmitting a light beam L1 radiated from the light beam source 12 without any diffraction in an outgoing optical path and diffracting a light beam L2 reflected on the information medium 12 in a returning optical path, an objective lens 15 for converging the light beam L1 transmitting through the hologram 13 on the information medium 14 to read the information, an actuator 16 for integrally moving the objective lens 15 with the blazed hologram 13 to focus the light beam L1 on the information medium 12 with the objective lens 15, and a photo detector 17 for detecting the intensity of the light beam L2 reflected on the information medium 12 to reproduce the information.
  • a light beam source 13 such as a semiconductor laser
  • a transmission type of blazed hologram 14 for transmitting a light beam L1 radiated from the light beam source 12 without any d
  • a relative position between the blazed hologram 14 and the objective lens 15 is fixed by a fixing means 18.
  • a blazed pattern is formed on a side of the objective lens 15 to integrally form the blazed hologram 14 with the objective lens 15.
  • a light beam L1 (or a laser beam) radiated from the light beam source 13 is radiated to the blazed hologram 14, and the light beam L1 mainly transmits through the blazed hologram 14 without any diffraction in an outgoing optical path.
  • the light beam L1 transmitting through the blazed hologram 14 is called zero-order diffracted light. Thereafter, the zero-order diffracted light L1 is converged on the information medium 12 by the objective lens 15. In the information medium 12, information indicated by a series of patterned pits is recorded and read by the zero-order diffracted light L1.
  • a beam light L2 having the information is reflected toward the objective lens 15 in a returning optical path and is incident to the blazed hologram 14.
  • the light L2 is mainly diffracted.
  • the light L2 diffracted is called first-order diffracted light.
  • the first-order diffracted light L2 is received in the photo detector 17.
  • the intensity distribution of the first-order diffracted light L2 is detected. Therefore, a servo signal for adjusting the position of the objective lens 15 by the action of the actuator 16 is obtained. Also, the intensity of the first-order diffracted light L2 is detected in the photo detector 17. Because the information medium 12 is rotated at high speed, the patterned pits radiated by the light 17 are changed so that the intensity of the first-order diffracted light L2 detected is changed. Therefore, an information signal indicating the information recorded in the information medium 12 is obtained by detecting the change in intensity of the first-order diffracted light L2.
  • a part of the light beam L1 is necessarily diffracted in the blazed hologram 14 when the light beam L1 is radiated to the blazed hologram 14 in the outgoing optical path. Therefore, unnecessary diffracted light such as first-order diffracted light and minus first-order diffracted light necessarily occurs.
  • the unnecessary diffracted light in the outgoing optical path also reads the information recorded in the information medium 12, and the unnecessary light is undesirably received in the photo detector 17.
  • the blazed hologram 14 is manufactured to form a blazed hologram pattern on the surface thereof, so that the intensity of the unnecessary light received in the photo detector 17 is decreased.
  • An optical disk having a high density memory capacity has been recently developed because of the improvement in a design technique of an optical system and the shortening of the wavelength of light radiated from a semiconductor laser.
  • a numerical aperture at an optical disk side of an imaging optical system in which a light beam converged on an optical disk is minutely narrowed in diameter is enlarged to obtain the optical disk having a high density memory capacity.
  • the degree of aberration occurring in the imaging optical system is increased because an optical axis of the system tilts from a normal line of the optical disk.
  • the numerical aperture is increased, the degree of the aberration is enlarged.
  • it is effective to thin the thickness of the optical disk.
  • the thickness of the optical disk denotes a distance from a surface of the optical disk (or an information medium) radiated by a light beam to an information recording plane on which a series of patterned pits are formed.
  • Fig. 3 shows a relationship between the thickness of the optical disk and the numerical aperture on condition that the tilt of the optical axis is constant.
  • the numerical aperture is 0.5 when the thickness of the optical disk is 1.2 mm, it is effective to thin the optical disk to 0.6 mm in thickness when the numerical aperture is increased to 0.6. In this case, even though the numerical aperture is increased on condition that the tilt of the optical axis is not changed, the degree of the aberration is not increased. Therefore, it is preferred that the thickness of the optical disk be thinned to obtain the optical disk having a high density memory capacity.
  • the thickness of a prospective optical disk having a high density memory capacity becomes thinner than that of a present optical disk such as a compact disk appearing on the market now.
  • the thickness of the compact disk is about 1.2 mm
  • the thickness of the prospective optical disk is expected to range from 0.4 mm to 0.8 mm.
  • it is required to record or reproduce information on or from an optical disk with an optical head system regardless of whether the optical disk is the present optical disk or the prospective optical disk having a high density memory capacity. That is, an optical head apparatus having an imaging optical system in which a light beam is converged on an optical disk within the diffraction limit regardless of whether the optical disk is thick or thin is required.
  • a piece of information is only recorded or reproduced on or from an optical disk having a fixed thickness.
  • an aberration such as a spherical aberration occurs when the optical head apparatus 11 is operated. Therefore, the recording or the reproduction of the information is impossible. Accordingly, there is a drawback that an optical head apparatus in which a piece of information is recorded or reproduced on or from an optical disk regardless of whether the optical disk is the present optical disk or the prospective optical disk having a high density memory capacity cannot be manufactured in a conventional technique.
  • EP-0 486 060 A discloses a recording/reproducing system which includes a compound objective lens having a hologram which focuses light of different frequencies onto respective different focal points.
  • a first object of the present invention is to provide, with due consideration to the drawbacks of conventional objective lenses having a focal point, an imaging optical system using a compound objective lens having two focal points.
  • a second object of the present invention is to provide an imaging optical system having the compound objective lens in which light transmitting through the compound objective lens is converged at a diffraction limit on two converging spots placed at different depths of an information medium.
  • a third object of the present invention is to provide an optical head apparatus having the imaging optical system in which information is recorded, reproduced or erased on or from one of the converging spots of the information medium at which light is converged by the action of the imaging optical system.
  • a fourth object of the present invention is to provide an optical disk apparatus in which information is recorded or reproduced on or from the optical disk with the compound objective lens regardless of whether a series of recording pits expressing pieces of information is recorded or reproduced on or from the high density optical disk having a thin thickness or a conventional compact disk having an ordinary thickness.
  • a fifth object of the present invention is to provide a focusing method for focusing light on an information medium with the optical head apparatus.
  • a sixth object of the present invention is to provide an information reproducing method for reproducing a piece of recording information recorded on a high density optical disk having a thin thickness.
  • a part of incident light transmits through the hologram means without any diffraction. Therefore, a beam of transmitted light not diverged from the hologram means or not converging is formed. Thereafter, the transmitted light is refracted and converged by the lens means, so that the transmitted light is focused on a first converging spot positioned at a first focal point.
  • a beam of diffracted light such as a beam of first-order diffracted light which is diverged from the hologram lens or converges is formed. Thereafter, the diffracted light is refracted and converged by the lens means, so that the diffracted light is focused on a second converging spot positioned at a second focal point.
  • the compound objective lens has two focal points, and the incident light transmitting through the compound objective lens are converged on two converging points.
  • the incident light transmitting through the compound objective lens can be reliably converged on an information medium regardless whether the information medium has a first thickness or a second thickness.
  • a grating pattern be drawn in the hologram means in a concentric circle shape, the grating pattern of the hologram means be formed in relief to concentrically form alternating rows of bottom portions and top portions, a height H of relief in the grating pattern be set to H ⁇ ⁇ /(n( ⁇ )-1) where a symbol ⁇ denotes a wavelength of the incident light and a symbol n( ⁇ ) denotes a refractive index of the hologram means made of a glass material for the incident light having the wavelength ⁇ , and a difference in phase modulation degree between the incident light transmitting through a bottom portion of the grating pattern and the incident light transmitting through a top portion of the grating pattern be lower than 2 ⁇ radians to set a diffraction efficiency of the hologram means to a value lower than 100 %.
  • the diffraction efficiency of the hologram means is set to a value lower than 100 % over the entire grating pattern, so that the transmitted light and the diffracted light are simultaneously formed in the hologram lens.
  • a beam of incident light is radiated from a light source.
  • a far field pattern of the incident light may be distributed to decrease intensity of the incident light toward a peripheral portion of the beam.
  • the light source is a semiconductor laser
  • the far field pattern of the incident light is distributed in the Gaussian distribution.
  • the incident light transmits through the hologram means.
  • the difference in phase modulation degree between the incident light transmitting through a bottom portion of the grating pattern and the incident light transmitting through a top portion of the grating pattern is induced to be lower than 2 ⁇ radians. Therefore, the diffraction efficiency of the hologram means for the incident light is set to a value lower than 100 % over the entire grating pattern, so that the transmitted light and the diffracted light are simultaneously formed in the hologram lens.
  • the diffraction efficiency of the hologram means for the incident light is gradually lowered toward the outer direction of the pattern region. Therefore, the incident light positioned at a center portion of its beam are mainly changed to the diffracted light, and the incident light positioned at a peripheral portion of its beam are mainly changed to the transmitted light.
  • the transmitted light is refracted and converged by the lens means, so that the transmitted light is focused on a first converging spot positioned at a first focal point.
  • the diffracted light is refracted and converged by the lens means, so that the diffracted light is focused on a second converging spot positioned at a second focal point.
  • the first focal point for the transmitted light differs from the second focal point for the diffracted light.
  • the far field pattern of the incident light is distributed in the Gaussian distribution
  • the far field pattern of the transmitted light is distributed in a gently-sloping shape. Therefore, secondary maxima (or side lobes) of the transmitted light can be prevented from occurring at the first converging spot.
  • a numerical aperture of the lens means for the diffracted light can be sufficiently heightened.
  • the diffraction efficiency of the hologram means for the incident light is gradually lowered toward the inner direction of the pattern region. Therefore, the incident light positioned at a center portion of its beam are mainly changed to the transmitted light, and the incident light positioned at a peripheral portion of its beam are mainly changed to the diffracted light.
  • the far field pattern of the incident light is distributed in the Gaussian distribution
  • the far field pattern of the diffracted light is distributed in a gently-sloping shape. Therefore, secondary maxima (or side lobes) of the diffracted light can be prevented from occurring at the second converging spot.
  • a numerical aperture of the lens means for the transmitted light can be sufficiently heightened.
  • a beam of incident light is radiated from the light source, and a part of the incident light transmits through the hologram lens to form a beam of transmitted light. Also, a remaining part of the incident light is diffracted by the hologram lens to form a beam of diffracted light. Thereafter, the transmitted light and the diffracted light are converged by the converging means.
  • the transmitted light is incident on the rear surface of the first information medium and is converged at the front surface of the first information medium to form the first converging spot.
  • the transmitted light is reflected at the rear surface of the first information medium and again passes through the lens means and the hologram means without any diffraction.
  • the diffracted light is incident on the rear surface of the second information medium and is converged at the front surface of the second information medium to form the second converging spot.
  • the diffracted light is reflected at the rear surface of the second information medium and again passes through the lens means.
  • the diffracted light is again diffracted by the hologram means.
  • a wavefront of the transmitted light or the diffracted light is changed by the wavefront changing means to form a plurality of beams of reflected light, and the intensities of the reflected light is detected by the detecting means. Therefore, an information signal expressing the information recorded on the first or second information medium is generated according to the intensities of the reflected light.
  • a compound objective lens composed of the hologram lens and the lens means has two focal points. Therefore, a piece of information can be recorded or reproduced on or from an information medium regardless of whether the information medium has the first thickness or the second thickness.
  • an optical head apparatus comprising the light source, the hologram means, the lens means and the detecting means has the same configuration as that described before. Initially, the optical head apparatus is moved by the moving means to converge in focus the diffracted light formed in the hologram means on the second substrate of the optical disk rotated by the rotating means. Therefore, the distinguishing information recorded on the second substrate is reproduced in the detecting means, and it is informed that pieces of recording information are recorded or reproduced on or from the first substrate having the first thickness. Thereafter, the optical head apparatus is moved by the moving means to converge in focus the transmitted light formed in the hologram means on the first substrate of the optical disk rotated by the rotating means. Therefore, a piece of recording information is recorded or reproduced on or from the first substrate of the optical disk.
  • the recording information can be reliably recorded or reproduced.
  • the optical head apparatus is moved by the moving means to converge in defocus the diffracted light formed in the hologram means on the second substrate of the optical disk rotated by the rotating means.
  • the distinguishing information is recorded at a low density, a plurality of recording pits expressing the distinguishing information are respectively large in size. Therefore, even though the diffracted light is converged on each of the recording pits in defocus, a converging spot of the diffracted light is formed in each of the recording pits. Therefore, the distinguishing information recorded on the second substrate is reproduced in the detecting means, and it is informed that pieces of recording information are recorded or reproduced on or from the first substrate having the thin thickness.
  • the optical head apparatus is moved by the moving means to converge in focus the transmitted light formed in the hologram means on the first substrate of the optical disk rotated by the rotating means. Therefore, a piece of recording information is recorded or reproduced on or from the first substrate of the optical disk.
  • a focusing method according to the invention is performed by utilizing the optical head apparatus described above.
  • the intensity of the focus error signal is largely increased when the distance between the lens means and the first or second information medium is near to a focal length of the lens means. Therefore, when the intensity of the focus error signal becomes larger than a threshold value, the lens means is placed near to a just-focus point in which the transmitted light or the diffracted light is converged on the first or second information medium in focus.
  • the transmitted light or the diffracted light can be focused on the first or second information medium.
  • An information reproducing method is performed by utilizing the optical disk apparatus described above.
  • the distinguishing information placed on the second substrate of the optical disk is reproduced with the diffracted light.
  • the optical disk apparatus is moved to a position under the first substrate of the optical disk, and the transmitted light is converged on the first substrate of the optical disk.
  • the diffracted light is just focused on the first substrate.
  • the recording information can be reliably reproduced.
  • Fig. 4A is a constitutional view of an imaging optical system having a compound objective lens according to a first embodiment of the present invention, a beam of transmitted light not diffracted being converged on a thin type of information medium.
  • Fig. 4B is a constitutional view of the imaging optical system shown in Fig. 4A, a beam of first-order diffracted light being converged on a thick type of information medium.
  • Fig. 5 is a plan view of a hologram lens shown in Figs. 4A, 4B, a grating pattern of the hologram lens being depicted.
  • an imaging optical system 21 for converging light on a first substrate 22 of a thin type of first information medium 23 (a thickness T1) or a second substrate 24 of a thick type of second information medium 25 (a thickness T2) to form a diffraction-limited converging spot comprises a blazed hologram lens 26 for transmitting a part of incident light L3 radiated from a light source without any diffraction to form a beam of transmitted light L4 and diffracting a remaining part of the incident light L3 to form a beam of first-order diffracted light L5, and an objective lens 27 for converging the transmitted light L4 on the first information medium 23 or converging the first-order diffracted light L5 on the second information medium 25.
  • the first information medium 23 represents a prospective optical disk having a high density memory capacity, and the thickness T1 of the first information medium 23 ranges from 0.4 mm to 0.8 mm.
  • the second information medium 25 represents a compact disk or a laser disk appearing on the market now, and the thickness T2 of the second information medium 25 is about 1.2 mm.
  • convergence denotes in this specification that divergent light or collimated light is focused to form a diffraction-limited micro spot.
  • a part of incident light L3 collimated transmits through the hologram lens 26 without any diffraction, and a beam of transmitted light L4 (that is, a beam of zero-order diffracted light L4) is formed. Thereafter, the transmitted light L4 is converged by the objective lens 27. Also, a remaining part of the incident light L3 is diffracted and refracted by the hologram lens 26, and a beam of first-order diffracted light L5 is formed.
  • the hologram lens 26 selectively functions as a concave lens for the first-order diffracted light L5, so that the first-order diffracted light L5 diverges from the hologram lens 26. Thereafter, the first-order diffracted light L5 is converged by the objective lens 27.
  • the transmitted light L4 is incident on a rear surface of the first information medium 23 and is focused on its front surface by the objective lens 27 to form a diffraction-limited converging spot S1 on the first information medium 23.
  • the diffracted light L5 is incident on a rear surface of the second information medium 25 and is focused on its front surface to form a diffraction-limited converging spot S2 on the second information medium 25.
  • a compound objective lens 29 composed of the hologram lens 26 and the objective lens 27 has substantially two focal points.
  • the hologram lens 26 is formed by drawing a grating pattern P1 in a pattern region 26A of a transparent substrate 28 in a concentric circle shape.
  • the pattern region 26A is positioned in a center portion of the transparent substrate 28, and a no-pattern region 26B is positioned in a peripheral portion of the transparent substrate 28 to surround the pattern region 26A.
  • An optical axis of the imaging optical system 21 passes through a central point of the grating pattern P1 and a central axis of the objective lens 27.
  • the grating pattern P1 of the hologram lens 26 is formed in relief to produce a phase modulation type of hologram lens. That is, blocks which each are composed of a bottom portion and a top portion are concentrically formed in the grating pattern P1.
  • the height H of the relief in the grating pattern P1 is set to: H ⁇ ⁇ /(n( ⁇ )-1), where the symbol ⁇ denotes a wavelength of the incident light L3 and the symbol n( ⁇ ) denotes a refractive index of the transparent substrate 28 for the incident light L3.
  • a difference in phase modulation degree between the incident light L3 transmitting through a bottom portion of the grating pattern P1 and the incident light L3 transmitting through a top portion of the grating pattern P1 is lower than 2 ⁇ radians. Therefore, a diffraction efficiency of the hologram lens 26 for the incident light L3 transmitting through the grating pattern P1 is less than 100 % to generate the light L4 transmitting through the grating pattern P1. Also, the incident light L3 transmitting through the no-pattern region 26B is not diffracted. As a result, the intensity of the transmitted light L4 can be sufficient to record or reproduce pieces of information on or from the first information medium 23.
  • the intensity of the transmitted light L4 is sufficient over the entire surface of the hologram lens 26, secondary maxima (side lobes) of the transmitted light L4 undesirably occurring in the converging spot S1 can be suppressed.
  • a primary maximum (a main lobe) of the transmitted light L4 positioned in a center of the converging spot S1 is utilized to record or reproduce a piece of information on or from the first information medium 23, and secondary maxima positioned around the primary maximum are unnecessary because the secondary maxima deteriorate a recording pit or a reproducing signal formed by the primary maximum.
  • the grating pattern P1 of hologram lens 26 formed in relief is blazed as shown in Fig. 6, so that the occurrence of minus first-order diffracted light is considerably suppressed. Therefore, the intensity sum of the transmitted light L4 and the first-order diffracted light L5 is maximized. In other words, a utilization efficiency of the incident light L3 is enhanced.
  • the numerical aperture NA of the objective lens 27 is equal to or more than 0.6. Also, when the transmitted light L4 is converged by the objective lens 27, the diffraction-limited converging spot S1 is formed on the first information medium 23 having a thickness T1.
  • a diameter of the hologram lens 26 is almost the same as an aperture of the objective lens 27, so that a diameter of the pattern region 26A is smaller than the aperture of the objective lens 27. Because the incident light L3 transmitting through the no-pattern region 26B is not diffracted, not only the light L4 transmitting through the pattern region 26A but also the light L4 transmitting through the no-pattern region 26B are converged on the first information medium 23 by the objective lens 27 having a high numerical aperture. Therefore, the intensity of the transmitted light L4 converged at the converging point S1 can be increased.
  • the incident light L3 transmitting through the pattern region 26A of the hologram lens 26 is changed to the first-order diffracted light L5, and the first-order diffracted light L5 is converged on the second information medium 25 by the objective lens 27 having substantially a low numerical aperture.
  • the phase of the light L4 transmitting through the grating pattern P1 of the pattern region 26A is determined by an average value of the phase modulation degrees in the light L4 transmitting through the bottom and top portions of the grating pattern P1.
  • the height of the no-pattern region 26B is constant, the phase of the light L4 transmitting through the no-pattern region 26B is modulated at a phase modulation degree. Therefore, as shown in Fig. 6, the height of the no-pattern region 26B is set even with an average height of the grating pattern P1 to enhance the convergence function of the objective lens 27.
  • each block of the grating pattern P1 in the hologram lens 26 shown in Fig. 6 approximates to a step-wise shape composed of four stairs
  • a first step is etched at a depth h1+h2 and a width W1
  • a second step is etched at a depth h1 and a width W2
  • a third step is etched at a depth h2 and a width W2
  • a fourth step is etched at a width W1. Therefore, the grating pattern P1 approximating to the step-wise shape is formed in the pattern region 26A.
  • the height of the no-pattern region 26B is almost the same as an average height of the pattern region 26A, so that the phase of the light L4 transmitting through the pattern region 26A is almost the same as that of the light L4 transmitting through the no-pattern region 26B.
  • an ideal blazed shape of the hologram lens 26 shown in Fig. 6 can approximate to a step-wise shape which is obtained by etching a center portion of the transparent substrate 28 many times.
  • the height H0 of the step-wise shape is set to satisfy an equation H0 ⁇ ⁇ /(n( ⁇ )-1) so that the difference in phase modulation degree is set to a value lower than 2 ⁇ radians.
  • the difference n o in level is set to satisfy an equation n o ⁇ ⁇ / ⁇ (n( ⁇ )-1)*N ⁇ to set the difference in phase modulation degree of each stairs to a value lower than 2 ⁇ /N radians.
  • a peripheral portion of the transparent substrate 28 is etched to set the thickness of the no-pattern region 26B to a thickness of the pattern region 26A at one of the N stairs which is not the top stair or the bottom stair.
  • the height of the no-pattern region 26B is almost the same as an average height of the pattern region 26A, so that the phase of the light L4 transmitting through the pattern region 26A is almost the same as that of the light L4 transmitting through the no-pattern region 26B.
  • the grating pattern P1 of the hologram lens 26 is designed to correct any aberration occurring in the objective lens 27 and the second information medium 25, so that the first-order diffracted light L5 transmits through the second information medium 25 having a thickness T2 and is converged on the medium 25 to form the diffraction-limited converging spot S2 without any aberration.
  • a method for designing the hologram lens 26 having an aberration correcting function is described.
  • the grating pattern P1 of the hologram lens 26 which agrees with the interference pattern calculated can be easily formed according to a computer generated hologram technique.
  • the compound objective lens 29 is composed of the objective lens 27 and the hologram lens 26 in which a part of the incident light L3 is diffracted and refracted, a diffraction-limited converging spot can be reliably formed on an information medium regardless of whether the information medium has a thickness T1 or a thickness T2. Also, two diffraction-limited converging spots can be simultaneously formed on an information medium at difference depths. In other words, the compound objective lens has substantially two focal points.
  • the diffraction efficiency of the hologram lens 26 is less than 100 % and the intensity of the light L4 transmitting through the hologram lens 26 is sufficient to record or reproduce information on or from the first information medium 23, the secondary maxima of the transmitted light L4 converged on the converging spot S1 can be suppressed.
  • the hologram lens 26 is blazed, the occurrence of minus first-order diffracted light can be considerably suppressed. Therefore, the intensity sum of the transmitted light L4 and the first-order diffracted light L5 can be maximized, and a utilization efficiency of the incident light L3 can be enhanced.
  • the hologram lens 26 functions as a lens only for the first-order diffracted light, the position of the converging point S1 formed by the transmitted light L4 differs from that of the converging point S2 formed by the first-order diffracted light L5 in an optical axis direction. Therefore, when the transmitted light L4 is converged in focus on an information recording plane of the information medium 23 to record or read a piece of information, the first-order diffracted light L5 converged on the information medium 23 is out of focus at the information recording plane. In the same manner, when the first-order diffracted light L5 is converged in focus on an information recording plane of the information medium 25, the transmitted light L4 converged on the information medium 25 is out of focus at the information recording plane.
  • the light L4 (or L5) when the light L4 (or L5) is converged on the converging spot S1 (or S2) in focus to record or read the information, the light L5 (or L4) not converged on the converging spot S1 (or S2) in focus does not adversely influence on the recording or reading of the information.
  • a difference in the optical axis direction between the converging spots S1, S2 is required to be equal to or more than 50 ⁇ m.
  • the light L5 (or L4) largely diverges to reduce the intensity of the light L5 (or L4) at an information recording plane when the light L4 (or L5) is converged on the converging spot S1 (or S2) of the information recording plane at a high intensity.
  • the difference in the optical axis direction between the converging points S1, S2 is required to be equal to or less than 1.0 mm by considering a moving range of an actuator with which the position of the compound objective lens 29 composed of the objective lens 27 and the hologram lens 26 is adjusted according to a focus servo signal. Because the hologram lens 26 functions as a concave lens for the first-order diffracted light, the difference between the converging points S1, S2 can be increased to about 1 mm.
  • the diffraction efficiency of the hologram lens 26 for changing the incident light L3 to the diffracted light L5 is set in a range from about 20 % to 70 %.
  • the intensity of the transmitted light L4 converged on the high density optical disk is almost the same as that of the first-order diffracted light L5 converged on the compact disk. Therefore, the output power of the incident light L3 can be minimized.
  • the diffraction efficiency of the hologram lens 26 for changing the incident light L3 to the first-order diffracted light L5 is set to a value equal to or lower than 30 %.
  • the recording of the information can be reliably performed without increasing the intensity of the incident light L3 because a transmission efficiency of the hologram lens 26 for the incident light L3 is high.
  • a utilization efficiency of the incident light L3 can be enhanced when a piece of information is recorded on the high density optical disk, so that the output power of the incident light L3 can be minimized.
  • the hologram lens 26 functions as a concave lens for the first-order diffracted light L5.
  • a hologram lens 26M functioning as a convex lens for the first-order diffracted light L5 be utilized in place of the hologram lens 26. That is, as shown in Figs. 9A, 9B, the diffracted light L5 is converged on the first information medium 23 by the objective lens 27 to form the diffraction limited converging spot S1, and the transmitted light L4 is converged on the second information medium 25 by the objective lens 27 to form the diffraction limited converging spot S2.
  • the difference between the converging points S1, S2 is required to be equal to or less than 0.5 mm by considering the moving range of the actuator.
  • the occurrence of a chromatic aberration can be prevented in an imaging optical system 21M in which the hologram lens 26M functioning as a concave lens for the diffracted light L5 is utilized.
  • the achromatization function in the imaging optical system is described in detail.
  • the focal length f H of the hologram lens 22 is shortened as the wavelength ⁇ of the incident light L3 becomes longer.
  • a refractive index of the objective lens 27 for the incident light L3 having a wavelength ⁇ o is represented by n( ⁇ o )
  • another refractive index of the objective lens 27 for the incident light L3 having a wavelength ⁇ l is represented by n( ⁇ l )
  • a focal length f D ( ⁇ ) of the objective lens 27 for the incident light L3 having a wavelength ⁇ is formulated by an equation (3).
  • f D ( ⁇ l ) f D ( ⁇ O ) ⁇ (n( ⁇ O ) - 1)/(n( ⁇ l ) - 1)
  • the focal length f D ( ⁇ ) of the objective lens 27 is lengthened as the wavelength ⁇ of the incident light L3 becomes longer. That is, the dependence of the focal length f D ( ⁇ ) on the wavelength ⁇ in the objective lens 27 is opposite to that of the focal length f H on the wavelength ⁇ in the hologram lens 26M. Therefore, a condition that the compound objective lens 29M composed of the objective lens 27 and the hologram lens 26M functions as an achromatic lens is formulated by an equation (4).
  • the compound objective lens 29M having an achromatic function can be formed by the combination of the lenses 26M, 27, and the occurrence of the chromatic aberration can be prevented. Also, even though the equation (4) is not strictly satisfied, the occurrence of the chromatic aberration can be largely suppressed.
  • a curvature of the objective lens 27 can be small because the hologram lens 26M functions as a convex lens for the first-order diffracted light L5. Also, because the hologram lens 26M is a plane type of element, a lightweight type of compound objective lens having an achromatic function can be made in large scale manufacture.
  • a principal of the achromatization has been proposed in a first literature (D. Faklis and M. Morris, Photonios Spectra(1991), November p.205 & December p.131), a second literature (M.A. Gan et al., S.P.I.E.(1991), Vol.1507, p.116), and a third literature (P. Twardowski and P. Meirueis, S.P.I.E.(1991), Vol.1507, p.55).
  • Fig. 10A is a constitutional view of an imaging optical system having a compound objective lens according to a second embodiment of the present invention, a beam of transmitted light not diffracted being converged on a thin type of information medium.
  • Fig. 10B is a constitutional view of the imaging optical system shown in Fig. 10A, a beam of first-order diffracted light being converged on a thick type of information medium.
  • an imaging optical system 31 for converging light on the first substrate 22 of the first information medium 23 (the thickness T1) or the second substrate 24 of the second information medium 25 (the thickness T2) to form a diffraction-limited converging spot comprises a blazed hologram lens 32 for transmitting a part of incident light L3 without any diffraction to form a beam of transmitted light L4 and diffracting a remaining part of incident light L3 to form a beam of first-order diffracted light L5, and the objective lens 27 for converging the transmitted light L4 on the first information medium 23 or converging the first-order diffracted light L5 on the second information medium 25.
  • the hologram lens 32 is formed by drawing a grating pattern P2 in a pattern region 32A of the transparent substrate 28 in a concentric circle shape.
  • the pattern region 32A is positioned in a center portion of the transparent substrate 28.
  • An diameter of the grating pattern P2 is equal to or larger than an aperture of the objective lens 27.
  • a diffraction efficiency of the hologram lens 32 for the incident light L3 transmitting through the grating pattern P2 is less than 100 % in the same manner as in the first embodiment, so that the intensity of the transmitted light L4 is sufficient to record or reproduce a piece of information on or from the first information medium 23.
  • the diffraction efficiency in a central portion of the pattern region 32A is high, and the diffraction efficiency is gradually decreased toward an outer direction of the pattern region 32A.
  • the height H of the relief in the grating pattern P2 is gradually lowered toward the outer direction of the pattern region 32A.
  • each block of the grating pattern P2 positioned in the central portion of the transparent substrate 28 is formed in a step-wise shape shown in Fig.
  • each block of the grating pattern P2 positioned in a peripheral portion of the transparent substrate 28 is formed in a step-wise shape shown in Fig. 12B in which an inclined angle ⁇ 2 of stairs is small and a relationship W1 ⁇ W2 between the etching widths is satisfied.
  • each block of the grating pattern P2 positioned in a middle portion between the central and peripheral portions is formed in a step-wise shape shown in Fig. 12C in which the etching widths W1, W2 is the same.
  • a part of the incident light L3 transmits through the hologram lens 32 without any diffraction to form a beam of transmitted light L4, and the transmitted light L4 is converged by the objective lens 27. Also, a remaining part of the incident light L3 is diffracted and refracted by the hologram lens 32.
  • the hologram lens 32 functions as a concave lens for the incident light L3, so that a first-order diffracted light L5 diverges from the hologram lens 32. Thereafter, the first-order diffracted light L5 is converged by the objective lens 27.
  • the transmitted light L4 is incident on a rear surface of the first information medium 23 and is focused on its front surface by the objective lens 27 to form a diffraction-limited converging spot S3 on the first information medium 23.
  • the diffraction efficiency in the central portion of the grating pattern P2 is high and because the diffraction efficiency is gradually decreased toward the outer direction of the grating pattern P2, a diffraction probability of the incident light L3 is lowered in the peripheral portion of the grating pattern P2. Therefore, the light L4 transmits through the objective lens 27 on condition that the numerical aperture NA of the objective lens 27 is high.
  • the diffracted light L5 is incident on a rear surface of the second information medium 25 and is focused on its front surface to form a diffraction-limited converging spot S5 on the second information medium 25.
  • the hologram lens 32 functions as a concave lens to diverge the first-order diffracted light L5, the diffraction-limited converging spots S3, S4 are formed even though the thickness T1 of the first information medium 23 differs from the thickness T2 of the second information medium 25. Therefore, a compound objective lens 34 composed of the hologram lens 32 and the objective lens 27 has substantially two focal points.
  • the intensity of the transmitted light L4 converged on the first information medium 23 can be high.
  • a far field pattern of the incident light L3 is distributed in a Gaussian distribution as shown in Fig. 13A. Therefore, because the diffraction efficiency is gradually decreased toward the outer direction of the grating pattern P2, a far field pattern of the transmitted light L4 is distributed in a gently-sloping shape as shown in Fig. 13B.
  • the intensity of the transmitted light L4 is suddenly increased at the peripheral portion of the hologram lens 26.
  • the diffraction efficiency of the hologram lens 32 is heightened to increase the intensity of the first-order diffracted light L5
  • the intensity of the transmitted light L4 at its inner beam portion is largely decreased, and secondary maxima (or side lobes) of the transmitted light L4 at the converging spot S3 is undesirably increased. Therefore, the incident light L3 of which the far field pattern is distributed in the Gaussian distribution is radiated to the hologram lens 32 to increase the intensity of the first-order diffracted light L5 without any increase of the second maxima.
  • the incident light L3 distributed not only in a central portion of the Gaussian distribution but also in a peripheral portion of the Gaussian distribution transmits through the hologram lens 32 and is refracted by the objective lens 27 because the diameter of the grating pattern P2 is equal to or larger than the aperture of the objective lens 27. Therefore, a numerical aperture NA of the objective lens 27 at a light source side for the incident light L3 becomes higher than that in the first embodiment, and the diffraction efficiency of the hologram lens 32 is heightened. As a result, the intensity of the first-order diffracted light L5 converged on the second information medium 25 can be increased, as shown in Fig. 14B.
  • intensity of the incident light L3 at the peripheral portion of the Gaussian distribution is low and because the diffraction efficiency of the hologram lens 32 is increased toward the inner direction of the grating pattern region 32A, intensity of the transmitted light L4 is distributed in a gently-sloping shape as shown in Fig. 14C. Accordingly, secondary maxima of the transmitted light L4 at the converging spot S3 can be suppressed.
  • the diffraction efficiency of the hologram lens 32 for the incident light L3 is set in a range from about 20 % to 70 %.
  • the intensity of the transmitted light L4 converged on the high density optical disk is almost the same as that of the first-order diffracted light L5 converged on the compact disk. Therefore, the output power of the incident light L3 can be minimized.
  • the diffraction efficiency of the hologram lens 32 for the incident light L3 is set to a value equal to or lower than 30 %.
  • the recording of the information can be reliably performed without increasing the intensity of the incident light L3 because a transmission efficiency of the hologram lens 32 for the incident light L3 is high.
  • a utilization efficiency of the incident light L3 can be enhanced when a piece of information is recorded on the high density optical disk, so that the output power of the incident light L3 can be minimized.
  • the grating pattern P2 positioned in the central portion of the transparent substrate 28 is gradually changed toward the outer direction of the pattern region 32A from the step-wise shape shown in Fig. 12A to the step-wise shape shown in Fig. 12B through the step-wise shape shown in Fig. 12C.
  • the middle portion occupy a large part of the pattern region 32A of the hologram lens 32.
  • the intensity sum of the transmitted light L4 and the first-order diffracted light L5 can be maximized, so that a utilization efficiency of the incident light L3 can be enhanced.
  • the grating pattern P2 formed in the step-wise shape shown in Fig. 12B be changed to a step-wise shape shown in Fig. 12D when the first width W1 is decreased to a value lower than about 1 ⁇ m. That is, a flight of four stairs shown in Fig. 12B is changed to a flight of two stairs. In this case, the grating pattern P2 formed in the step-wise shape shown in Fig. 12D can be easily made.
  • the grating pattern P2 be formed in a step-wise shape shown in Fig. 12E. That is, a third etching width W3 is gradually decreased toward the outer direction of the pattern region 32A while decreasing a height H5 of the grating pattern P2. Therefore, the diffraction efficiency of the hologram lens 32 can be gradually decreased toward the outer direction of the pattern region 32A without any manufacturing difficulty of the grating pattern P2.
  • a hologram lens 33 be formed, in place of the hologram lens 32, by placing the grating pattern P1 of the pattern region 32A in a central portion of the transparent substrate 28 and placing four types of diffraction regions 33A, 33B, 33C and 33D which surround the grating pattern P1.
  • a part of the incident light L3 transmitting through each of the diffraction regions 33A to 33D is diffracted to control a transmission efficiency of the hologram lens 33.
  • the intensity of the transmitted light L4 at its peripheral portion is decreased, so that secondary maxima occurring in the converging spot S3 can be suppressed.
  • the grating pattern P1 of the hologram be replaced with the grating pattern P2. Also, it is applicable that grating directions of the diffraction regions 33A to 33D differ from each other. In this case, even though the first-order diffracted light L5 diffracted in the diffraction region 33A is, for example, incident on the diffraction region 33c after the diffracted light L5 is reflected by the second information medium 25, the diffracted light L5 again diffracted in the diffraction region 33c does not pass in parallel to the optical axis.
  • the first-order diffracted light L5 diffracted in the diffraction regions 33A to 33D is not detected by the detector as stray light. Accordingly, the reproduction of the information does not deteriorate.
  • the hologram lens 32 function as a convex lens.
  • the diffracted light L5 is converged on the first information medium 23, and the transmitted light L4 is converged on the second information medium 25, as shown in Fig. 15C.
  • Fig. 16A is a constitutional view of an imaging optical system having a compound objective lens according to a third embodiment of the present invention, a beam of first-order diffracted light being converged on a thin type of information medium.
  • Fig. 16B is a constitutional view of the imaging optical system shown in Fig. 16A, a beam of transmitted light not diffracted being converged on a thick type of information medium.
  • an imaging optical system 41 for converging light on the first substrate 22 of the first information medium 23 (the thickness T1) or the second substrate 24 of the second information medium 25 (the thickness T2) to form a diffraction-limited converging spot comprises a blazed hologram lens 42 for transmitting a part of incident light L3 without any diffraction to form a beam of transmitted light L4 and diffracting a remaining part of incident light L3 to form a beam of first-order diffracted light L6, and the objective lens 27 for converging the first-order diffracted light L6 on the first information medium 23 or converging the transmitted light L4 on the second information medium 25.
  • the hologram lens 42 is formed by drawing a grating pattern P3 in a pattern region 42A of the transparent substrate 28 in a concentric circle shape.
  • the pattern region 42A is positioned in a center portion of the transparent substrate 28.
  • An diameter of the grating pattern P3 is equal to or larger than an aperture of the objective lens 27.
  • a diffraction efficiency of the hologram lens 42 for the incident light L3 transmitting through the grating pattern P3 is less than 100 % in the same manner as in the first embodiment, so that the intensity of the transmitted light L4 is sufficient to record or reproduce a piece of information on or from the second information medium 25.
  • the diffraction efficiency of the hologram lens 42 is high in a peripheral portion of the pattern region 42A, and the diffraction efficiency is gradually decreased toward an inner direction of the pattern region 42A.
  • the height H of the relief in the grating pattern P3 is gradually lowered toward the inner direction of the pattern region 42A.
  • each pitch of the grating pattern P3 positioned in the peripheral portion of the transparent substrate 28 is formed in a step-wise shape shown in Fig.
  • each pitch of the grating pattern P3 positioned in a central portion of the transparent substrate 28 is formed in a step-wise shape shown in Fig. 12B in which the inclined angle ⁇ 2 of stairs is small and the relationship W1 ⁇ W2 is satisfied.
  • each pitch of the grating pattern P3 positioned in a middle portion between the central and peripheral portions is formed in a step-wise shape shown in Fig. 12C in which the etching widths W1, W2 is the same.
  • a part of the incident light L3 transmits through the hologram lens 42 without any diffraction to form a beam of transmitted light L4, and the transmitted light L4 is converged by the objective lens 27.
  • a remaining part of the incident light L3 is diffracted by the hologram lens 42 to form a beam of first-order diffracted light L6.
  • the hologram lens 42 functions as a convex lens for the incident light L3, so that a first-order diffracted light L6 formed in the hologram lens 42 converges. Thereafter, the diffracted light L6 is converged by the objective lens 27.
  • the diffracted light L6 is incident on a rear surface of the first information medium 23 and is focused on its front surface to form a diffraction-limited converging spot S5 on the first information medium 23.
  • the transmitted light L4 is incident on a rear surface of the second information medium 25 and is focused on its front surface to form a diffraction-limited converging spot S6 on the second information medium 25.
  • a compound objective lens 43 composed of the hologram lens 42 and the objective lens 27 has substantially two focal points.
  • the hologram lens 42 functions as a convex lens for the diffracted light L6, the diffracted light L6 transmits through the objective lens 27 on condition that the numerical aperture NA of the objective lens 27 is substantially high.
  • the grating pattern P3 of the hologram lens 42 is designed to correct any aberration occurring in the objective lens 27 and the first information medium 23, so that the diffracted light L6 transmits through the first information medium 23 having the thickness T1 and is converged on the medium 23 to form the diffraction-limited converging spot S5 without any aberration.
  • a method for designing the hologram lens 42 having an aberration correcting function is described.
  • the diffracted light L6 After the diffracted light L6 is converged on the first information medium 23, spherical waves diverge from the converging spot S5 and transmit through the first substrate 22 and the objective lens 27. Thereafter, the spherical waves transmit through the transparent substrate 28 and optically interfere with the incident light L3. Therefore, an interference pattern is formed by the interference between the spherical waves and the incident light L3.
  • the interference pattern can be calculated by adding the phase of the spherical waves to an inverted phase obtained by inverting the phase of the incident light L3. Accordingly, the grating pattern P3 of the hologram lens 42 which agrees with the interference pattern calculated can be easily formed according to a computer generated hologram technique.
  • the hologram lens 42 functions as a convex lens for the first-order diffracted light L6, a curvature of the objective lens 27 can be lowered. Also, a glass material having a high refractive index is not required to produce the objective lens 27.
  • the distance in an optical axis direction between the converging spots S5, S6 can be lengthened to about 1 mm. Therefore, even though the transmitted light L4 (or the first-order diffracted light L6) is converged on the converging spot S6 (or S5) in focus to record or read a piece of information, the light L6 (or L4) is not converged on the converging spot S6 (or S5) in focus to reduce the intensity of the light L6 (or L4) at the converging spot S6 (or S5). Accordingly, no adverse influence is exerted on the recording or reproduction of the information
  • the hologram lens 42 functions as a convex lens for the first-order diffracted light L6, the occurrence of a chromatic aberration can be prevented in the imaging optical system 41.
  • the focal length of the hologram lens 42 is shortened as the wavelength of the incident light L3 becomes longer.
  • the focal length of the objective lens 27 is lengthened as the wavelength of the incident light L3 becomes longer. That is, the dependence of the focal length on the wavelength in the objective lens 27 is opposite to that of the focal length on the wavelength in the hologram lens 42. Therefore, the compound objective lens 43 having an achromatic function can be formed by the combination of the lenses 27, 42, and the occurrence of the chromatic aberration can be prevented.
  • the hologram lens 42 is a plane type of element, a lightweight type of compound objective lens can be made in large scale manufacture.
  • the numerical aperture of the objective lens 27 for the first-order diffracted light L6 becomes substantially enlarged. Therefore, the intensity of the first-order diffracted light L6 can be enlarged to record or reproduce a piece of information on or from the first information medium 23.
  • a far field pattern of the incident light L3 is distributed in a Gaussian distribution as shown in Fig. 13A. Therefore, because the diffraction efficiency of the hologram lens 42 is gradually decreased toward the inner direction of the grating pattern P2, a far field pattern of the first-order diffracted light L6 is distributed in a gently-sloping shape. Accordingly, secondary maxima of the first-order diffracted light L6 converged on the converging spot S5 can be moreover suppressed in the third embodiment as compared with in the first embodiment. That is, the recording and reproducing of the information can be performed without any deterioration of the information by utilizing the imaging optical system 41.
  • the incident light L3 of which the far field pattern is distributed in the Gaussian distribution is radiated to the hologram lens 42 to increase the intensity of the transmitted light L4 without any increase of the second maxima.
  • the incident light L3 distributed in not only a central portion of the Gaussian distribution but also a peripheral portion of the Gaussian distribution transmits through the hologram lens 42 and is refracted by the objective lens 27 because the diameter of the grating pattern P3 is equal to or larger than the aperture of the objective lens 27. Therefore, a numerical aperture NA of the objective lens 27 at a light source side for the incident light L3 becomes higher than that in the first embodiment, and a transmission efficiency of the hologram lens 42 is heightened.
  • the intensity of the transmitted light L4 converged on the second information medium 25 can be increased, as shown in Fig. 18B.
  • the intensity of the incident light L3 at the peripheral portion of the Gaussian distribution is low and because the diffraction efficiency of the hologram lens 42 is decreased toward the inner direction of the grating pattern 42A, the first-order diffracted light L6 is distributed in a gently-sloping shape as shown in Fig. 18C. Accordingly, secondary maxima of the first-order diffracted light L6 at the converging spot S5 can be suppressed.
  • the diffraction efficiency of the hologram lens 42 for the incident light L3 is set in a range from about 20 % to 70 %.
  • the intensity of the transmitted light L4 converged on the compact disk is almost the same as that of the first-order diffracted light L6 converged on the high density optical disk. Therefore, the output power of the incident light L3 can be minimized.
  • the diffraction efficiency of the hologram lens 42 for the incident light L3 is set to a value equal to or higher than 55 %.
  • the recording of the information can be reliably performed without increasing the intensity of the incident light L3 because the diffraction efficiency of the hologram lens 42 for changing the incident light L3 to the first-order diffracted light L6 is high.
  • a utilization efficiency of the incident light L3 can be enhanced when a piece of information is recorded on the high density optical disk, so that the output power of the incident light L3 can be minimized.
  • the diffraction efficiency of the hologram lens 42 is gradually decreased toward an inner direction of the pattern region 42A, the numerical aperture of the objective lens 27 for the first-order diffracted light L6 becomes substantially enlarged. Therefore, the intensity of the first-order diffracted light L6 can be enlarged to record or reproduce a piece of information on or from the high density optical disk.
  • the grating pattern P3 positioned in the pattern region 42A of the transparent substrate 28 is gradually changed toward the outer direction of the pattern region 42A from the step-wise shape shown in Fig. 12B to the step-wise shape shown in Fig. 12A through the step-wise shape shown in Fig. 12C while increasing the height H of the grating pattern P3.
  • the middle portion occupy a large part of the pattern region 42A of the hologram lens 42. In this case, the intensity sum of the transmitted light L4 and the first-order diffracted light L6 can be maximized, so that a utilization efficiency of the incident light L3 can be enhanced.
  • the first etching width W1 of the grating pattern P3 is gradually decreased toward the inner direction of the pattern region 42A, it is applicable that the grating pattern P3 formed in the step-wise shape shown in Fig. 12B be changed to a step-wise shape shown in Fig. 12D when the first width W1 is decreased to a value lower than about 1 ⁇ m. In this case, the grating pattern P3 formed in the step-wise shape shown in Fig. 12D can be easily made. In addition, in cases where a height H4 of the grating pattern P3 formed in the step-wise shape shown in Fig.
  • the grating pattern P3 be formed in a step-wise shape shown in Fig. 12E.
  • a third etching width W3 is gradually decreased toward the inner direction of the pattern region 42A while decreasing a height H5 of the grating pattern P3. Therefore, the diffraction efficiency of the hologram lens 42 can be gradually decreased toward the inner direction of the pattern region 42A without any manufacturing difficulty of the grating pattern P3.
  • the grating patterns P1, P2 and P3 of the hologram lenses 26, 32 and 42 are respectively formed on a front side of the transparent substrate 28 not facing the objective lens 27. Therefore, a beam of light reflected at the front side of the transparent substrate 28 does not adversely influence as stray light on the recording or reproduction of the information. In detail, because the reflected light is diffracted by the hologram lens, the reflected light is scattered. Also, even though the first-order diffracted light L5 or L6 is reflected at a reverse side of the transparent substrate 28, the diffracted light reflected is again diffracted by the hologram lens and is scattered. Therefore, the light reflected at the front or reverse side of the hologram lens does not adversely influence on the recording or reproduction of the information.
  • the grating patterns P1, P2 and P3 of the hologram lenses 26, 32 and 42 be respectively formed on a reverse side of the transparent substrate 28 facing the objective lens 27.
  • the design of the image optical systems 21, 31 and 41 can be simplified.
  • the grating patterns P1, P2 and P3 of the hologram lenses 26, 32 and 42 are respectively formed in relief to produce a phase modulation type of hologram lens.
  • the phase modulation type of hologram lens can be produced by utilizing a liquid crystal cell.
  • the phase modulation type of hologram lens can be produced by utilizing a birefringece material such as lithium niobate.
  • the phase modulation type of hologram lens can be produced by proton-exchanging a surface part of a lithium niobate substrate.
  • the compound objective lens 29, 34 or 43 having two focal points is composed of the objective lens 27 and the hologram lens 26, 32 or 42.
  • a compound objective lens according to a fourth embodiment is shown in Fig. 19A, it is preferred that each of the hologram lenses 26, 32 and 42 and the objective lens 27 be unified with a packaging means 44 to form a compound objective lens 45 in which a relative position between each of the hologram lenses 26, 32 and 42 and the objective lens 27 is fixed.
  • the transmitted light L4 and the first-order diffracted light L5, L6 can be easily converged on the first or second information medium 23, 25 by adjusting the position of the packing means 44 with an actuator.
  • each of the grating patterns P1, P2 and P3 be directly drawn on a curved side of the objective lens 27 facing a light source side to form a compound objective lens 46 in which each of the hologram lenses 26, 32 and 42 is integrally formed with the objective lens 27.
  • the central axis of the objective lens 27 can always agree with that of each of the hologram lenses 26, 32 and 42, so that abaxial aberrations of each of the hologram lenses 26, 32 and 42 such as a coma aberration and an astigmatic aberration occurring in the first-order diffracted light can be prevented in the fourth embodiment.
  • each of the grating patterns P1, P2 and P3 be directly drawn on a side of the objective lens 27 facing the information medium 23 or 25 to form a compound objective lens 47 in which each of the hologram lenses 26, 32 and 42 is integrally formed with the objective lens 27.
  • a curvature at the side of the objective lens 27 can be small or in a plane shape. Therefore, each of the grating patterns P1, P2 and P3 can be made at a low cost.
  • the aberration can be prevented by fixing the hologram lens and a light source of the incident light L3 on the same base.
  • FIG. 21 An optical head apparatus with one of the compound objective lenses 29, 29M, 34, 43, 45, 46 and 47 shown in the first to fifth embodiments is described with reference to Figs. 21 to 26 according to a sixth embodiment of the present invention.
  • X, Y and Z co-ordinates shown in Figs. 21 to 26 are utilized in common.
  • Fig. 21 is a constitutional view of an optical head apparatus according to a sixth embodiment.
  • an optical head apparatus 51 for recording or reproducing pieces of information on or from the information medium 23 or 25, comprises a light source 52 such as a semiconductor laser for radiating the incident light L3, a collimator lens 53 for collimating the incident light L3, a beam splitter 54 for transmitting the incident light L3 on an outgoing optical path and reflecting a beam of transmitted light L4R formed by reflecting the transmitted light L4 on the information medium 23 or 25 or a beam of diffracted light L5R (or L6R) formed by reflecting the diffracted light L5 (or L6) on the information medium 23 or 25 on an incoming optical path, the compound objective lens 29 (or 29M, 34, 43, 45, 46 or 47) composed of the hologram lens 26 (or 26M, 32, 33 or 42) and the objective lens 27, a converging lens 55 for converging the transmitted light L4R or the diffracted light L5R reflected by the beam splitter 54, a wavefront changing device 56 such as a hologram for changing a wave
  • a beam of incident light L3 radiated from the light source 52 is collimated in the collimator lens 53 and transmits through the beam splitter 54. Thereafter, a part of the incident light L3 transmits through the compound objective lens 29 without any diffraction, and a remaining part of the incident light L3 is diffracted.
  • the transmitted light L4 is converged on the first information medium 23 to form the first converging spot S1. That is, the transmitted light L4 is incident on a rear surface of the first information medium 23, and the first converging spot S1 is formed on a front surface of the first information medium 23. Thereafter, a beam of transmitted light L4R reflected at the front surface of the first information medium 23 passes through the same optical path in the reverse direction. That is, a part of the transmitted light L4R again transmits through the compound objective lens 29 without any diffraction and is reflected by the beam splitter 54. In this case, the transmitted light L4R is collimated.
  • the transmitted light L4R is converged by the converging lens 55, and the wavefront of a large part of the transmitted light L4R is changed to form a plurality of converging spots on the photo detector 57. Thereafter, the intensities of the converging spots of the transmitted light L4R are detected in the photo detector 57. Therefore, an information signal and servo signals such as a focus error signal and a tracking error signal are obtained.
  • the actuating unit 58 are operated according to the servo signals to move the compound objective lens 29 at high speed, so that the transmitted light L4 is converged on the first information medium 23 in focus.
  • the diffracted light L5 is converged on the second information medium 25 to form the second converging spot S2. That is, the diffracted light L5 is incident on a rear surface of the second information medium 25, and the second converging spot S2 is formed on a front surface of the second information medium 25. Thereafter, a beam of diffracted light L5R reflected at the front surface of the second information medium 25 passes through the same optical path in the reverse direction. That is, a part of the diffracted light L5R is again diffracted by the hologram lens 26 and is reflected by the beam splitter 54. In this case, the diffracted light L5R is collimated.
  • the diffracted light L5R is converged by the converging lens 55, and the wavefront of a large part of the diffracted light L5R is changed to form a plurality of converging spots on the photo detector 57.
  • the diffracted light L5R incident on the converging lens 55 is collimated in the same manner as the transmitted light L4R incident on the converging lens 55, the converging spots of the diffracted light L5R are formed at the same positions as those of the transmitted light L4R.
  • the intensities of the converging spots of the diffracted light L5R are detected in the photo detector 57. Therefore, an information signal and servo signals such as a focus error signal and a tracking error signal are obtained.
  • the actuating unit 58 are operated according to the servo signals to move the compound objective lens 29 at high speed, so that the diffracted light L5 is converged on the second information medium 25 in focus.
  • a converging spot S7 on the photo detector 57 at which the light L4R or L5R not diffracted by the wavefront changing device 56 is converged relates to a radiation point of the light source 52 in a mirror image, so that the light L4R and L5R not diffracted by the wavefront changing device 56 are converged at the same converging point S7.
  • the light L4R and L5R diffracted by the wavefront changing device 56 are converged at the same other converging points.
  • the wavefront changing unit 56 and the photo detector 57 required to detect the intensity of the transmitted light L4R can be utilized to detect the intensity of the diffracted light L5R. Therefore, the number of parts required to manufacture the optical head apparatus 51 can be reduced, and a small sized optical head apparatus can be manufactured at a low cost and in light weight even though pieces of information are recorded or reproduced on or from an information medium by utilizing the optical head apparatus 51 regardless of whether the information medium is thick or thin.
  • each of the compound objective lenses 45, 46 and 47 can be manufactured in light weight because the hologram lens 26 (or 32, 33, 42) is a plane type of optical device.
  • the hologram lens 26 (or 32, 33, 42) is less than several tens mg in weight. Therefore, the hologram lens 26 integrally formed with the objective lens 27 can be easily moved by the actuating unit 58.
  • Fig. 22 is a plan view of the wavefront changing unit 56.
  • Fig. 23 is an enlarged view of first-order diffracted light and transmitted light detected in the photo detector 57.
  • the wavefront changing unit 56 is partitioned into a diffracted light generating region 56a in which a grating pattern P4 is drawn and a pair of diffracted light generating regions 56b, 56c in which a pair of grating patterns P5, P6 are drawn.
  • the light L4R or L5R incident on the diffracted light generating region 56a is diffracted to obtain a focus error signal.
  • the light L4R or L5R incident on each of the diffracted light generating regions 56b, 56c is diffracted to obtain a tracking error signal.
  • a spot size detection method utilized to detect a focus error signal is described as an example of a detecting method of a focus error signal.
  • the method is proposed in Japanese Patent Application No. 185722 of 1990.
  • an allowable assembly error in an optical head apparatus can be remarkably enlarged, and the servo signal such as a focus error signal can be stably obtained to adjust the position of the compound objective lens even though the wavelength of the incident light L3 varies.
  • the grating pattern P4 is designed to change the transmitted light L4R (or the diffracted light L5R) transmitting through the diffracted light generating region 56a of the wavefront changing unit 56 to a beam of first-order diffracted light L7 and a beam of minus first-order diffracted light L8.
  • the diffracted light L7, L8 are expressed by two types of spherical waves having different curvatures.
  • interference fringes are produced by actually interfering a spherical wave having a focal point FP1 in the front of the photo detector 57 with another spherical wave diverging from the converging spot S7 according to a two-beam interferometric process, so that the grating pattern P4 agreeing with the interference fringes is formed.
  • the interference fringes are calculated according to a computer generated hologram method.
  • the transmitted light L4R (or the diffracted light L5R) transmitting through the diffracted light generating region 56a of the wavefront changing unit 56 is diffracted and changed to beams of conjugate diffracted light such as a beam of first-order diffracted light L7 and a beam of minus first-order diffracted light L8.
  • the beam of first-order diffracted light L7 has the focal point FP1 at the front surface of the photo detector 57
  • the beam of minus first-order diffracted light L8 has a focal point FP2 in the rear of the photo detector 57.
  • the photo detector 57 comprises a sextant photo-detector 59 (or a six-division photo detector) in which six detecting sections SE1, SE2, SE3, SE4, SE5 and SE6 are provided.
  • the intensity of the first-order diffracted light L7 is detected by each of the detecting sections SE1, SE2 and SE3 of the sextant photo-detector 59 and is changed to electric current signals SC1, SC2 and SC3.
  • the intensity of the minus first-order diffracted light L8 is detected by each of the detecting sections SE4, SE5 and SE6 of the sextant photo-detector 59 and is changed to electric current signals SC4, SC5 and SC6.
  • Fig. 25A and 25C respectively show a converging spot of the first-order diffracted light L7 radiated to the detecting sections SE1, SE2 and SE3 of the sextant photo-detector 59 and another converging spot of the minus first-order diffracted light L8 radiated to the detecting sections SE4, SE5 and SE6 of the sextant photo-detector 59 on condition that the objective lens 27 is defocused on the information medium 23 or 25.
  • Fig. 25A and 25C respectively show a converging spot of the first-order diffracted light L7 radiated to the detecting sections SE1, SE2 and SE3 of the sextant photo-detector 59 and another converging spot of the minus first-order diffracted light L8 radiated to the detecting sections SE4, SE5 and SE6 of the sextant photo-detector 59 on condition that the objective lens 27 is defocused on the information medium 23 or 25.
  • 25B shows a converging spot of the first-order diffracted light L7 radiated to the detecting sections SE1, SE2 and SE3 of the sextant photo-detector 59 and another converging spot of the minus first-order diffracted light L8 radiated to the detecting sections SE4, SE5 and SE6 of the sextant photo-detector 59 on condition that the objective lens 27 is just focused on the information medium 23 or 25.
  • a converging spot S8 of the diffracted light L7 shown at the left side of Figs. 25A, 25C is formed on the sextant photo-detector 59, and another converging spot S9 of the diffracted light L8 shown at the right side of Fig. 25A or 25C is formed on the sextant photo-detector 59.
  • the intensity of the diffracted light L7 is detected in each of the detecting sections SE1, SE2 and SE3 of the sextant photo-detector 59 and is changed to electric current signals SC1, SC2, SC3. Also, the intensity of the diffracted light L8 is detected in the detecting sections SE4, SE5 and SE6 of the sextant photo-detector 59 and is changed to electric current signals SC4, SC5 and SC6. Thereafter, a focus error signal S fe is obtained according to the spot size detection method by calculating an equation (5).
  • the diffracted light L7, L8 are expressed by two types of spherical waves having different curvatures to detect the focus error signal S fe .
  • two beams of diffracted light L7, L8 radiated to the photo detector 57 are not limited to the spherical waves. That is, because the change of the diffracted light L7, L8 in a Y-direction is detected by the photo detector 57 according to the spot size detection method, it is required that a one-dimensional focal point of the diffracted light L7 is positioned in the front of the photo detector 57 and a one-dimensional focal point of the diffracted light L8 is positioned in the rear of the photo detector 57. Therefore, it is applicable that diffracted light including astigmatic aberration be radiated to the photo detector 57.
  • an information signal S in is obtained by adding all of the electric current signals according to an equation (6).
  • S in SC1 + SC2 + SC3 + SC4 + SC5 + SC6
  • the information medium 23 or 25 is rotated at high speed, a patterned track pit radiated by the converging spots S8, S9 of the diffracted light L7,L8 is rapidly changed one after another, so that the intensity of the information signal S in is changed. Therefore, the information stored in the information medium 23 or 25 can be reproduced according to the information signal S in .
  • the grating pattern P5 drawn in the diffracted light generating region 56b shown in Fig. 22 is designed to change the transmitted light L4R (or the diffracted light L5R) transmitting through the diffracted light generating region 56b of the wavefront changing unit 56 to a beam of first-order diffracted light L9 and a beam of minus first-order diffracted light L10. Also, the grating pattern P6 drawn in the diffracted light generating region 56c shown in Fig.
  • the 22 is designed to change the transmitted light L4R (or the diffracted light L5R) transmitting through the diffracted light generating region 56c of the wavefront changing unit 56 to a beam of first-order diffracted light L11 and a beam of minus first-order diffracted light L12.
  • the photo detector 57 further comprises four tracking photo-detectors 60a to 60d for detecting intensities of the diffracted light L9 to L12.
  • the intensity of the diffracted light L9 is detected by the tracking photo-detector 60a and is changed to an electric current signal SC7
  • the intensity of the diffracted light L10 is detected by the tracking photo-detector 60d and is changed to an electric current signal SC10
  • the intensity of the diffracted light L11 is detected by the tracking photo-detector 60b and is changed to an electric current signal SC8
  • the intensity of the diffracted light L12 is detected by the tracking photo-detector 60c and is changed to an electric current signal SC9.
  • a tracking error signal S te is calculated according to an equation (7).
  • S te SC7 - SC8- SC9 + SC10
  • the asymmetry of the intensity distribution of the transmitted light L4R (or the diffracted light L5R) incident on the wavefront changing unit 56 which changes in dependence on the positional relation between the converging spot S1 (or S2) and a patterned track pit radiated by the light L4 or L5, is expressed by the tracking error signal S te .
  • the objective lens 27 is moved in a radial direction so as to reduce a tracking error indicated by the tracking error signal S te .
  • the radial direction is defined as a direction perpendicular to both the optical axis and a series of patterned track pits. Therefore, the converging spot S1 (or S2) of the transmitted light L4 (or the diffracted light L5) on the information medium 23 (or 25) can be formed in the middle of the patterned track pit, so that the tracking error becomes zero.
  • the wavefront changing unit 56 has a wavefront changing function, a focus error signal can be easily obtained. Also, because the diffracted light generating regions 56b, 56c are provided in the wavefront changing unit 56, a tracking error signal can be easily obtained. Therefore, the number of parts required to manufacture the optical head apparatus 51 can be reduced, and the number of manufacturing steps can be reduced. In addition, the optical head apparatus can be manufactured at a low cost and in light weight.
  • the compound objective lens having two focal points is utilized in the optical head apparatus 51, pieces of information can be reliably recorded or reproduced from an information medium by utilizing the optical head apparatus 51 regardless of whether the information medium is thick or thin.
  • Fig. 27 is a constitutional view of an optical head apparatus according to a seventh embodiment.
  • an optical head apparatus 61 for recording or reproducing pieces of information on or from the information medium 23 or 25, comprises the light source 52, the collimator lens 53, the beam splitter 54, the compound objective lens 29 (or 29M, 34, 43, 45, 46 or 47) composed of the hologram lens 26 (or 26M, 32, 33 or 42) and the objective lens 27, the actuating unit 58, the converging lens 55, an astigmatic aberration generating unit 62 such as a plane parallel plate for generating an astigmatic aberration in the transmitted light L4R or the diffracted light L5R converged by the converging lens 55, and a photo detector 63 for detecting the intensity of the transmitted light L4R or the diffracted light L5R in which the astigmatic aberration is generated to obtain an information signal and servo signals such as a focus error signal and a tracking error signal.
  • the astigmatic aberration generating unit 62 is classified into one of the wavefront changing unit 56 because a wavefront of the transmitted light L4R or the diffracted light L5R is changed by the generating unit 62 to generate the astigmatic aberration in the light L4R or L5R. Also, a normal line of the unit 62 is tilted from an optical axis.
  • the photo detector 63 comprises a quadrant photo-detector 64 in which four detecting sections SE7, SE8, SE9 and SE10 are provided.
  • the transmitted light L4R (or the diffracted light L5R) reflected by the information medium 23 (or 25) is converged by the converging lens 55 in the same manner as in the sixth embodiment. Thereafter, the transmitted light L4R (or the diffracted light L5R) transmits through the astigmatic aberration generating unit 62 and is converged on the photo detector 57 to form a converging spot S10 on the detecting sections SE7, SE8, SE9 and SE10 of the quadrant photo-detector 64.
  • the transmitted light L4R (or the diffracted light L5R) converged by the converging lens 55 is a spherical wave
  • an astigmatic aberration is generated in the transmitted light L4R (or the diffracted light L5R) by the astigmatic aberration generating unit 62. Therefore, as shown in Figs. 29A to 29C, the shape of the converging spot S10 considerably changes depending on a distance between the compound objective lens 29 and the information medium 23 (or 25).
  • the converging spot S10 of the transmitted light L4R is formed on the quadrant photo-detector 64 as shown in Figs. 29A, 29C.
  • the converging spot S10 of the transmitted light L4R is formed on the quadrant photo-detector 64 as shown in Fig. 25B.
  • the intensity of the transmitted light L4R (or the diffracted light L5R) is detected in the detecting sections SE7, SE8, SE9 and SE10 of the quadrant photo-detector 64 and is changed to electric current signals SC11, SC12, SC13 and SC14. Thereafter, a focus error signal S fe is obtained according to an astigmatic aberration method by calculating an equation (8).
  • S fe (SC11 + SC14) - (SC12 + SC13)
  • the position of the compound objective lens 29 is moved in a direction parallel to an optical axis at high speed so as to minimize the absolute value of the focus error signal S fe .
  • a tangential direction Dt agreeing with an extending direction of patterned recording pits and a radial direction Dr perpendicular to both the optical axis and the patterned recording pits are defined as shown in Fig. 29D.
  • a tracking error signal S te is calculated according to an equation (9) by utilizing an intensity distribution change of the transmitted light L4R (or the diffracted light L5R) which depends on a positional relation between the converging spot S10 and a recording pit radiated by the light L4 or L5.
  • S te SC11 + SC13 - (SC12 + SC14)
  • the objective lens 27 is moved in the radial direction so as to reduce a tracking error indicated by the tracking error signal S te . Therefore, the converging spot S1, (or S2) of the transmitted light L4 (or the diffracted light L5) on the information medium 23 (or 25) can be formed in the middle of the recording pit, so that the tracking error becomes zero.
  • the tracking error signal S te is obtained according to a phase difference method by utilizing the result calculated in the equation (8).
  • an information signal S in is obtained by adding all of the electric current signals according to an equation (10).
  • S in SC11 + SC12 + SC13 + SC14
  • focus and tracking servo characteristics can be stably obtained in the optical head apparatus 61. That is, because an astigmatic aberration is generated in the transmitted light L4R (or the diffracted light L5R) by the astigmatic aberration generating unit 62 made of a plane parallel plate, the servo signals such as a focus error signal and a tracking error signal can be easily obtained. Therefore, the number of parts required to manufacture the optical head apparatus 61 can be reduced, and the number of manufacturing steps can be reduced. In addition, the optical head apparatus 61 can be manufactured at a low cost and in light weight.
  • the compound objective lens having two focal points is utilized in the optical head apparatus 61, pieces of information can be reliably recorded or reproduced from an information medium by utilizing the optical head apparatus 61 regardless of whether the information medium is thick or thin.
  • the astigmatic aberration generating unit 62 formed out of the plane parallel plate is arranged between the converging lens 55 and the photo detector 63.
  • an optical head apparatus 65 is shown in Fig. 30, it is applicable that a cylindrical lens 66 integrally formed with the converging lens 55 be arranged in place of the plane parallel plate to generate an astigmatic aberration in the transmitted light L4R (or the diffracted light L5R).
  • the cylindrical lens 66 is integrally formed with the converging lens 55, the optical head apparatus can be moreover manufactured at low cost.
  • a normal line of the hologram lens 26 (or 32, 33, 42) be tilted from an optical axis passing through the center of the objective lens 27 by about one degree to prevent stray light reflected in a surface of the hologram lens 26 from being incident on the photo detector 57 or 63. Also, it is applicable that the hologram lens 26 (or 32, 33, 42) be coated with an anti-reflection coating to prevent the occurrence of stray light.
  • a polarized beam splitter 68 be arranged in place of the beam splitter 54 to perfectly transmit the incident light L3 and a 1/4- ⁇ plate 69 be additionally placed between the hologram lens 26 (or 32, 33, 42) and the polarized beam splitter 68.
  • the incident light L3 transmits through the 1/4- ⁇ plate 69 in an outgoing optical path and because the transmitted light L4R (or the diffracted light L5R) again transmits through the 1/4- ⁇ plate 69 in an incoming optical path, the transmitted light L4R (or the diffracted light L5R) is perfectly reflected by the polarized beam splitter 68. Accordingly, a utilization efficiency of the incident light L3 can be enhanced. Also, a signal-noise ratio of each of the servo signals and the information signal can be enhanced.
  • the polarized beam splitter 68 be arranged in place of the beam splitter 54 to perfectly transmit the incident light L3 and the 1/4- ⁇ plate 69 be additionally placed between the hologram lens 26 (or 32, 33, 42) and the objective lens 27.
  • the transmitted light L4R (or the diffracted light L5R) is perfectly reflected by the polarized beam splitter 68 in the same manner as the optical head apparatus shown in Fig. 31.
  • the stray light reflected from the hologram lens 26 (or 32, 33, 42) transmits through the polarized beam splitter 68, the stray light is not incident on the photo detector 63. Accordingly, a signal-noise ratio of each of the servo signals and the information signal can be moreover enhanced.
  • a wedge-like prism 72 for reshaping the incident light L3 radiated from the light source 52 be additionally placed between the collimator lens 53 and the polarized beam splitter 68.
  • an elliptic wavefront of the incident light L3 is reshaped to a circular wavefront by the wedge-like prism 72. Accordingly, a utilization efficiency of the incident light L3 can be enhanced.
  • the transmitted light L4 that is, zero-order diffracted light L4
  • converged on the first information medium 23 is reflected toward the compound objective lens to reproduce a piece of information recorded on the first information medium 23
  • a part of the transmitted light L4R is diffracted in the hologram lens 26 (or 32, 33, 42) on the incoming optical path, so that the part of the transmitted light L4R is changed to a beam of first-order diffracted light L13. Therefore, the first-order diffracted light L13 diverges from the hologram lens 26, and a converging spot S11 of the diffracted light L13 is formed on the photo detector 57 or 63 in a relatively large size, as shown in Fig. 34.
  • the size of the converging spot S11 is larger than those of the sextant photo-detector 59 and the quadrant photo-detector 64. Therefore, there is a drawback that a signal-noise ratio in the information signal deteriorates.
  • the photo detector 57 (or 63) further comprise an information photo-detector 73 surrounding the sextant photo-detector 59 (or the quadrant photo-detector 64).
  • the size of the information photo-detector 73 is equal to or larger than a 1mm square. Therefore, in cases where the information signal is determined by the sum of the intensity of the transmitted light L4 detected in the sextant photo-detector 59 (or the quadrant photo-detector 64) and the intensity of the diffracted light L13 detected in the information photo-detector 73, the signal-noise ratio in the information signal can be enhanced, and frequency characteristics of the information signal can be enhanced.
  • Fig. 35A graphically shows a change of the focus error signal obtained by detecting the intensity of the transmitted light L4 formed in the hologram lens 26, 32 or 33, the strength of the focus error signal depending on a distance between the objective lens 27 and the first information medium 23.
  • Fig. 35B graphically shows a change of the focus error signal obtained by detecting the intensity of the diffracted light L5 formed in the hologram lens 26, 32 or 33, the strength of the focus error signal depending on a distance between the objective lens 27 and the second information medium 25.
  • the intensity of the transmitted light L4 is high because the numerical aperture of the objective lens 27 for the transmitted light L4 is large. Therefore, as shown in Fig. 35A, a change of a focus error signal FE1 obtained in cases where the objective lens 27 is almost focused on the first information medium 23 is considerably large as compared with a change of an unnecessary focus error signal FE2 obtained in cases where the objective lens 27 is defocused on the first information medium 23.
  • the unnecessary focus error signal FE2 is generated when the distance between the objective lens 27 and the first information medium 23 is larger than the focal length of the objective lens 27 for the transmitted light L4.
  • the intensity of the diffracted light L5 is comparatively low because the numerical aperture of the objective lens 27 for the diffracted light L5 is comparatively small. Therefore, as shown in Fig. 35B, a change of a focus error signal FE3 obtained in cases where the objective lens 27 is almost focused on the second information medium 25 is almost the same as that of an unnecessary focus error signal FE4 obtained in cases where the objective lens 27 is defocused on the second information medium 25.
  • the unnecessary focus error signal FE4 is generated when the distance between the objective lens 27 and the second information medium 25 is smaller than the focal length of the objective lens 27 for the diffracted light L5.
  • the objective lens 27 placed far from the first information medium 23 is gradually brought near to the first information medium 23. Thereafter, when the strength of the focus error signal reaches a threshold value, a focus servo loop provided in the photo detector 57 or 63 is set to an operation condition, so that the objective lens 27 is set to be focused on the first information medium 23. Also, in cases where the focusing of the diffracted light L5 on the second information medium 25 is performed, the objective lens 27 placed far from the second information medium 25 is gradually brought near to the second information medium 25 in the same manner. Thereafter, when the strength of the focus error signal reaches a threshold value, a focus servo loop provided in the photo detector 57 or 63 is set to an operation condition, so that the objective lens 27 is set to be focused on the second information medium 25.
  • the inverse influence of the unnecessary focus error signal FE4 on the focusing of the diffracted light L5 can be prevented.
  • the objective lens 27 placed far from the information medium 23 or 25 is gradually brought near to the information medium 23 or 25 regardless of whether the information medium is T1 or T2 in thickness
  • a focusing operation in each of the optical head apparatuses 51, 61, 65, 67, 70 and 71 with the hologram lens 26, 32 or 33 can be performed according to a common procedure by changing the threshold value or performing an auto gain control in which the focus error signal is normalized by detecting the total intensity of the transmitted light L4R or the diffracted light L5R. Therefore, a control circuit required to perform the focusing operation can be made at a low cost.
  • Fig. 36A graphically shows a change of the focus error signal obtained by detecting the intensity of the diffracted light L6 formed in the hologram lens 42, the strength of the focus error signal depending on a distance between the objective lens 27 and the first information medium 23.
  • Fig. 36B graphically shows a change of the focus error signal obtained by detecting the intensity of the transmitted light L4 formed in the hologram lens 42, the strength of the focus error signal depending on a distance between the objective lens 27 and the second information medium 25.
  • a change of a focus error signal FE5 obtained in cases where the objective lens 27 is almost focused on the first information medium 23 is considerably large as compared with a change of an unnecessary focus error signal FE6 obtained in cases where the objective lens 27 is defocused on the first information medium 23.
  • the unnecessary focus error signal FE6 is generated when the distance between the objective lens 27 and the first information medium 23 is smaller than the focal length of the objective lens 27 for the diffracted light L6.
  • a change of a focus error signal FE7 obtained in cases where the objective lens 27 is almost focused on the second information medium 25 is almost the same as that of an unnecessary focus error signal FE8 obtained in cases where the objective lens 27 is defocused on the second information medium 25.
  • the unnecessary focus error signal FE8 is generated when the distance between the objective lens 27 and the second information medium 25 is larger than the focal length of the objective lens 27 for the transmitted light L4.
  • the objective lens 27 placed near to the first information medium 23 is gradually moved away from the first information medium 23. Thereafter, when the strength of the focus error signal reaches a threshold value, a focus servo loop provided in the photo detector 57 or 63 is set to an operation condition, so that the objective lens 27 is set to be focused on the first information medium 23. Also, in cases where the focusing of the transmitted light L4 on the second information medium 25 is performed, the objective lens 27 placed near to the second information medium 25 is gradually moved away from the second information medium 25 in the same manner. Thereafter, when the strength of the focus error signal reaches a threshold value, a focus servo loop provided in the photo detector 57 or 63 is set to an operation condition, so that the objective lens 27 is set to be focused on the second information medium 25.
  • the inverse influence of the unnecessary focus error signal FE8 on the focusing of the transmitted light L4 can be prevented.
  • the objective lens 27 placed near to the information medium 23 or 25 is gradually moved away from the information medium 23 or 25 regardless of whether the information medium is T1 or T2 in thickness, a focusing operation in each of the optical head apparatuses 51, 61, 65, 67, 70 and 71 with the hologram lens 42 can be performed according to a common procedure by changing the threshold value or performing the auto gain control. Therefore, a control circuit required to perform the focusing operation can be made at a low cost.
  • Fig. 37 is a constitutional view of an optical head apparatus according to a ninth embodiment.
  • an optical head apparatus 81 for recording or reproducing pieces of information on or from the information medium 23 or 25, comprises the light source 52, the collimator lens 53, the beam splitter 54, the compound objective lens the compound objective lens 29 (34, 45, 46 or 47) composed of the hologram lens 26 (or 32 or 33) and the objective lens 27, the actuating unit 58, the converging lens 55, a beam splitter 82 for transmitting a beam of diffracted light L5R or reflecting a beam of transmitted light L4R, the photo detector 63 for detecting the intensity of the diffracted light L5R transmitting through the beam splitter 82 to obtain servo signals and an information signal recorded on the second information medium 25, the wavefront changing device 56 such as a hologram for changing a wavefront of the transmitted light L4R reflected by the beam splitter 82, and the photo detector 57 for detecting the intensity of the transmitted light L4R to obtain servo signals and an information signal recorded on the first information medium 23.
  • the beam splitter 82 is made of a plane parallel plate of which a normal line is tilted from an optical path, so that an astigmatic aberration is generated in the diffracted light L5R passing through the beam splitter 82. Also, a coating is applied on a surface of the plane parallel plate.
  • the transmitted light L4 (or the diffracted light L5) are converged by the converging lens 27 in the same manner as in the sixth embodiment. Thereafter, in cases where a piece of information is recorded or reproduced on or from the first information medium 23, the transmitted light L4 is converged on the first information medium 23 to form the first converging spot S1. Thereafter, a beam of transmitted light L4R reflected by the first information medium 23 passes through the same optical path in the reverse direction. That is, a great part of the transmitted light L4R again transmits through the compound objective lens without any diffraction and is reflected by the beam splitter 54.
  • the transmitted light L4R is converged by the converging lens 55, and a part of the transmitted light L4R is reflected by the beam splitter 82.
  • the wavefront of a great part of the transmitted light L4R is changed by the wavefront changing unit 56, and the great part of the transmitted light L4R is converged on the photo detector 57 to form the converging spots S8, S9. Therefore, an information signal and servo signals such as a focus error signal and a tracking error signal are obtained in the same manner as in the sixth embodiment.
  • a remaining part of the transmitted light L4R not changed its wavefront is converged on the photo detector 57 to form the converging spot S7.
  • the diffracted light L5 is converged on the second information medium 25 to form the second converging spot S2.
  • a beam of diffracted light L5R reflected by the second information medium 25 passes through the same optical path in the reverse direction, and a great part of the diffracted light L5R transmits through the hologram lens 26 without any diffraction. Therefore, the diffracted light L5R passes through the incoming optical path differing from the outgoing optical path. Thereafter, the diffracted light L5R is reflected by the beam splitter 54 and is converged by the converging lens 55.
  • a part of the diffracted light L5R transmits through the beam splitter 82.
  • an astigmatic aberration is generated in the diffracted light L5R.
  • the diffracted light L5R is converged on the photo detector 63 to form a converging spot S12 of which the shape is the same as the converging spot S10 shown in Figs. 29A to 29C, and the intensity of the diffracted light L5R is detected in the photo detector 63. Therefore, an information signal and servo signals such as a focus error signal and a tracking error signal are obtained in the same manner as in the seventh embodiment.
  • the remaining part of the transmitted light L4R transmits through the beam splitter 82, the remaining part of the transmitted light L4R is not converged at the converging spot S12 because the transmitted light L4R passes through the same optical path. Also, though a remaining part of the diffracted light L5R is reflected the beam splitter 82, the remaining part of the diffracted light L5R is not converged at the converging spot S7, S8 or S9 because the diffracted light L5R passes through the incoming optical path differing from the outgoing optical path.
  • the converging spot S12 formed on the photo detector 63 does not relate to a radiating point of the light source 52 in a mirror image, while the converging spot S7 formed on the photo detector 57 relates to the radiating point of the light source 52 in the mirror image.
  • a focal point of the diffracted light L5R converged by the converging lens 55 differs from that of the transmitted light L4R converged by the converging lens 55. Therefore, the photo detector 57 for detecting the intensity of the transmitted light L4R and the photo detector 63 for detecting the intensity of the diffracted light L5R are required.
  • the compound objective lens having two focal points is utilized in the optical head apparatus 81, pieces of information can be reliably recorded or reproduced on or from an information medium regardless of whether the information medium is thick or thin.
  • the diffraction efficiency of the hologram lens 26, 32 or 33 in the compound objective lens 29, 34, 45, 46 or 47 for changing a beam of light to a beam of first-order diffracted light is set to a value equal to or lower than 30 %.
  • a signal-noise ratio of each of the servo signals and the information signal obtained in the photo detector 63 can be enhanced because the diffracted light L5R transmitting through the hologram lens 26, 32 or 33 at a high transmission efficiency is utilized to obtain the servo signals and the information signal.
  • a utilization efficiency of the incident light L3 can be enhanced when a piece of information recorded on the thick type of optical disk 25 is reproduced, so that the output power of the incident light L3 can be minimized.
  • the recording of the information can be reliably performed without increasing the intensity of the incident light L3 because a transmission efficiency of the hologram lens 26, 32 or 33 for the incident light L3 is high. Also, in cases where a piece of information recorded on the high density optical disk 23 is reproduced in the photo detector 57, a signal-noise ratio of each signal obtained in the photo detector 57 can be enhanced because the transmission efficiency of the hologram lens 26, 32 or 33 for the light L3, L4R is high.
  • FIG. 38, 39 An optical head apparatus with the compound objective lens 29, 34, 45, 46 or 47 in which the incident light L3 is efficiently utilized to obtain an information signal and servo signals is described with reference to Figs. 38, 39 according to a tenth embodiment of the present invention.
  • X1 and Y1 co-ordinates shown in Figs. 38, 39 are utilized in common.
  • Fig. 38 is a constitutional view of an optical head apparatus according to a tenth embodiment.
  • Fig. 39 is a plan view of a beam splitter having a reflection type of hologram utilized in the optical head apparatus shown in Fig. 38.
  • an optical head apparatus 91 for recording or reproducing pieces of information on or from the information medium 23 or 25, comprises the light source 52, the collimator lens 53, the beam splitter 54, the compound objective lens 29 (or 34, 45, 46 or 47) composed of the hologram lens 26 (or 32 or 33) and the objective lens 27, the actuating unit 58, the converging lens 55, a beam splitter 92 having a reflection type of hologram 93 for transmitting a large part of the transmitted light L4R or reflecting all of the diffracted light L5R incident on the hologram 93, the photo detector 63 for detecting the intensity of the transmitted light L4R transmitting through the beam splitter 92 to obtain servo signals and an information signal recorded in the first information medium 23, and the photo detector 57 for detecting the intensity of the diffracted light L5R to obtain servo signals and an information signal recorded in the second information medium 25.
  • the beam splitter 92 is made of a plane parallel plate inclined to an optical path, so that an astigmatic aberration is generated in the transmitted light L4R passing through the beam splitter 92. Also, as shown in Fig. 39, the reflection type of hologram 93 is arranged at a center portion of the beam splitter 92, and a light transmitting region 92a is arranged at a peripheral portion of the beam splitter 92 to surround the hologram 93. Light incident on the light transmitting region 92a transmits without any diffraction.
  • the hologram 92 is partitioned into a diffracted light generating region 93a in which a grating pattern P7 is drawn and a pair of diffracted light generating regions 93b, 93c in which a pair of grating patterns P8, P9 are drawn.
  • the diffracted light L5R incident on the diffracted light generating region 93a is diffracted to obtain a focus error signal in the photo detector 57.
  • the diffracted light L5R incident on each of the diffracted light generating regions 93b, 93c is diffracted to obtain a tracking error signal in the photo detector 57.
  • the transmitted light L4 and the diffracted light L5 are converged by the converging lens 27 in the same manner as in the sixth embodiment. Thereafter, in cases where a piece of information is recorded or reproduced on or from the first information medium 23, the transmitted light L4 is converged on the first information medium 23 to form the first converging spot S1. Thereafter, a beam of transmitted light L4R reflected by the first information medium 23 passes through the same optical path in the reverse direction. That is, a large part of the transmitted light L4R again transmits through the compound objective lens 29 without any diffraction and is reflected by the beam splitter 54.
  • the transmitted light L4R is converged by the converging lens 55, and a large part of the transmitted light L4R transmits through the beam splitter 92.
  • an astigmatic aberration is generated in the transmitted light L4R.
  • the transmitted light L4R is converged on the photo detector 63 to form a converging spot S13 of which the shape is the same as the converging spot S10 shown in Figs. 29A to 29C, and the intensity of the transmitted light L4R is detected in the photo detector 63. Therefore, an information signal and servo signals such as a focus error signal and a tracking error signal are obtained in the same manner as in the seventh embodiment.
  • the diffracted light L5 is converged on the second information medium 25 to form the second converging spot S2.
  • a beam of diffracted light L5R reflected by the second information medium 25 passes through the same optical path in the reverse direction, and a large part of the diffracted light L5R transmits through the hologram lens 26 without any diffraction. Therefore, the diffracted light L5R transmits on the incoming optical path differing from the outgoing optical path in the same manner as in the ninth embodiment.
  • the diffracted light L5R is reflected by the beam splitter 54 and is converged by the converging lens 55 on the beam splitter 92 to form a converging spot on the reflection type of hologram 93 of the beam splitter 92. Therefore, all of the diffracted light L5R is diffracted and reflected by the hologram 93 to be converged on the photo detector 57. That is, the diffracted light L5R diffracted and reflected in the diffracted light generating region 93a of the hologram 93 is splitted into two beams and is converged on the detecting sections SE1 to SE6 of the sextant photo-detector 59 in the photo detector 57 in the same manner as in the sixth embodiment.
  • the diffracted light L5R diffracted and reflected in the diffracted light generating region 93b of the hologram 93 is splitted into two beams, and the intensity of the diffracted light L5R is detected in the tracking photo-detectors 60a and 60d.
  • the diffracted light L5R diffracted and reflected in the diffracted light generating region 93c of the hologram 93 is splitted into two beams, and the intensity of the diffracted light L5R is detected in the tracking photo-detectors 60b and 60c. Therefore, an information signal and servo signals such as a focus error signal and a tracking error signal are obtained in the same manner as in the sixth embodiment.
  • the converging spot S13 formed on the photo detector 63 does not relate to a radiating point of the light source 52 in a mirror image. Therefore, the photo detector 57 for detecting the intensity of the diffracted light L5R and the photo detector 63 for detecting the intensity of the transmitted light L4R are required.
  • the compound objective lens having two focal points is utilized in the optical head apparatus 91, pieces of information can be reliably recorded or reproduced on or from an information medium regardless of whether the information medium is thick or thin.
  • the diffracted light L5R can be utilized at high efficiency. Therefore, a signal-noise ratio of the signals obtained in the photo detector 57 can be enhanced.
  • the diffraction efficiency of the hologram lens 26, 32 or 33 in the compound objective lens 29, 34, 45, 46 or 47 for changing a beam of light to a beam of first-order diffracted light is set to a value equal to or lower than 30 %.
  • a signal-noise ratio of each of the servo signals and the information signal obtained in the photo detector 57 can be enhanced because the diffracted light L5R transmitting through the hologram lens 26, 32 or 33 at a high transmission efficiency is utilized to obtain the servo signals and the information signal.
  • a utilization efficiency of the incident light L3 can be enhanced when a piece of information recorded on the thick type of optical disk 25 is reproduced, so that the output power of the incident light L3 can be minimized.
  • the recording of the information can be reliably performed without increasing the intensity of the incident light L3 because a transmission efficiency of the hologram lens 26, 32 or 33 for the incident light L3 is high. Also, in cases where a piece of information recorded on the high density optical disk 23 is reproduced in the photo detector 63, a signal-noise ratio of each signal obtained in the photo detector 63 can be enhanced because the transmission efficiency of the hologram lens 26, 32 or 33 for the light L3, L4R is high.
  • FIG. 40 An optical head apparatus with the compound objective lens 29, 34, 45, 46 or 47 in which the incident light L3 is efficiently utilized to obtain an information signal and servo signals is described with reference to Figs. 40 to 42 according to an eleventh embodiment of the present invention.
  • X1 and Y1 co-ordinates shown in Figs. 40, 41 are utilized in common, and X, Y and Z co-ordinates shown in Figs. 40, 42 are utilized in common.
  • Figs. 40A, 40B are respectively a constitutional view of an optical head apparatus according an eleventh embodiment.
  • Fig. 41 is a plan view of a beam splitter having a reflection type of hologram utilized in the optical head apparatus shown in Fig. 38.
  • an optical head apparatus 101 for recording or reproducing pieces of information on or from the information medium 23 or 25, comprises the light source 52, the collimator lens 53, the beam splitter 54, the compound objective lens 29 (or 34, 45, 46 or 47) composed of the hologram lens 26 (or 32 or 33) and the objective lens 27, the actuating unit 58, the converging lens 55, a beam splitter 102 having a transmission type of hologram 103 for transmitting the transmitted light L4R converged on the first information medium 23 and the diffracted light L5R converged on the second information medium 25 and diffracting the transmitted light L4R which is converged on the second information medium 25 in defocus, a photo detector 104 for detecting the intensity of the transmitted light L4R converged on the first information medium 23 to obtain servo signals and an information signal recorded in the first information medium 23, detecting in defocus the intensity of the diffracted light L5R to obtain an information signal recorded in the second information medium 25, and
  • the beam splitter 102 is made of a plane parallel plate inclined to an optical path, so that an astigmatic aberration is generated in the light L4R, L5R passing through the beam splitter 102.
  • the transmission type of hologram 103 is arranged at a center portion of the beam splitter 102, and a light transmitting region 102a is arranged at a peripheral portion of the beam splitter 102 to surround the hologram 103.
  • the transmitted light L4R incident on the light transmitting region 102a transmits without any diffraction.
  • the hologram 102 is partitioned into diffracted light generating regions 103a, 103b alternately arranged to detect a focus error signal according to the spot size detection method described in the sixth embodiment.
  • a grating pattern P10 is drawn in each of the diffracted light generating regions 103a, and a converging spot is formed by the transmitted light L4R diffracted in the regions 103a.
  • a grating pattern P11 is drawn in each of the diffracted light generating regions 103b, and another converging spot is formed by the transmitted light L4R diffracted in the regions 103b.
  • the photo detector 104 comprises the sextant photo-detector 59 in which the detecting sections SE1, SE2, SE3, SE4, SE5 and SE6 are provided in the same manner as the photo detector 57.
  • the transmitted light L4 and the diffracted light L5 are converged by the converging lens 27 in the same manner as in the sixth embodiment. Thereafter, in cases where a piece of information is recorded or reproduced on or from the first information medium 23, as shown in Fig. 40A, the transmitted light L4 is converged on the first information medium 23 to form the first converging spot S1. Thereafter, a beam of transmitted light L4R reflected by the first information medium 23 passes through the same optical path in the reverse direction. That is, the transmitted light L4R again transmits through the compound objective lens without any diffraction and is reflected by the beam splitter 54.
  • the transmitted light L4R is converged by the converging lens 55, and a major part of the transmitted light L4R transmits through the beam splitter 103.
  • an astigmatic aberration is generated in the transmitted light L4R.
  • the transmitted light L4R is converged on the photo detector 104 to form a converging spot S14 of which the shape is the same as the converging spot S10 shown in Figs. 29A to 29C, and the intensity of the transmitted light L4R is detected in the photo detector 104. Therefore, an information signal and servo signals such as a focus error signal and a tracking error signal are obtained in the same manner as in the seventh embodiment.
  • the transmitted light L4R is converged on the photo detector 104 just in focus.
  • the diffracted light L5 is converged on the second information medium 25 to form the second converging spot S2.
  • a beam of diffracted light L5R reflected by the second information medium 25 passes through the same optical path in the reverse direction and transmits through the hologram lens 26 without any diffraction. Therefore, the diffracted light L5R transmits on the incoming optical path differing from the outgoing optical path in the same manner as in the ninth embodiment.
  • the diffracted light L5R is reflected by the beam splitter 54 and is converged by the converging lens 55.
  • the diffracted light L5R transmits through the beam splitter 102, and the diffracted light L5R is converged on the photo detector 57.
  • an astigmatic aberration is generated in the diffracted light L5R.
  • the position of the photo detector 104 detecting the diffracted light L5R does not relate to the radiation point of the light source 52 in the mirror image. Therefore, the diffracted light L5R is converged on the photo detector 104 in defocus.
  • an information signal is obtained in the same manner as in the seventh embodiment.
  • the transmitted light L4 is converged on the second information medium 25 in defocus as shown in Fig. 40B. That is, the transmitted light L4 incident on the rear surface of the second information medium 25 is converged at the front surface of the second information medium 25. Thereafter, a beam of transmitted light L4R reflected at the front surface of the second information medium 25 again transmits through the compound objective lens without any diffraction and is reflected by the beam splitter 54. Thereafter, the transmitted light L4R is converged by the converging lens 55 on the beam splitter 102 to form a converging spot on the of hologram 103 of the beam splitter 102.
  • the transmitted light L4R is diffracted by the hologram 103 and is converged on the photo detector 104. That is, the transmitted light L4R diffracted in the diffracted light generating regions 103a of the hologram 103 is changed to a first spherical wave SW1 of which a focal point is placed at the front of the photo detector 104, and the transmitted light L4R diffracted in the diffracted light generating regions 103b of the hologram 103 is changed to a second spherical wave SW2 of which a focal point is placed at the rear of the photo detector 104. Thereafter, as shown in Figs.
  • the first spherical wave SW1 is converged on the detecting sections SE1 to SE3 of the sextant photo-detector 59 in the photo detector 104 to form a converging spot S15A
  • the second spherical wave SW2 is converged on the detecting sections SE4 to SE6 of the sextant photo-detector 59 to form a converging spot S15B. Because the regions 103a, 103b are divided into many pieces, the converging spots S15A, S15B are respectively divided into many pieces.
  • the converging spots S15A, S15B of the transmitted light L4R shown in Figs. 42A, 42C are formed on the sextant photo-detector 59.
  • the converging spots S15A, S15B of the transmitted light L4R shown in Fig. 42B are formed on the sextant photo-detector 59.
  • the intensity of the transmitted light L4R is detected in each of the detecting sections SE1 to SE6 of the sextant photo-detector 59 and is changed to electric current signals SC15 to SC20.
  • a focus error signal S fe is obtained according to the spot size detection method by calculating an equation (11).
  • S fe (SC15 + SC17 - SC16) - (SC18 + SC20 - SC19)
  • the position of the compound objective lens is moved in a direction along an optical axis at high speed so as to minimize the absolute value of the focus error signal S fe . Therefore, the focus error signal is obtained in the same manner as in the sixth embodiment.
  • the compound objective lens having two focal points is utilized in the optical head apparatus 101, pieces of information can be reliably recorded or reproduced on or from an information medium regardless of whether the information medium is thick or thin.
  • the transmitted light L4R can be utilized at high efficiency. Therefore, a signal-noise ratio of the focus error signal obtained in the photo detector 104 can be enhanced.
  • the information signal and the servo signals can be obtained in the photo detector 104 regardless of whether the information medium 23 or 25 is thin or thick. Therefore, the number of parts required to manufacture the optical head apparatus 101 can be reduced, and a small sized optical head apparatus can be manufactured at a low cost and in light weight even though pieces of information are recorded or reproduced on or from an information medium by utilizing the optical head apparatus 101 regardless of whether the information medium is thick or thin.
  • the diffraction efficiency of the hologram lens 26, 32 or 33 in the compound objective lens 29, 34, 45, 46 or 47 is set to a value equal to or lower than 30 %.
  • a signal-noise ratio of each of the servo signals and the information signal obtained in the photo detector 104 can be enhanced because the diffracted light L5R transmitting through the hologram lens 26, 32 or 33 at a high transmission efficiency is utilized to obtain the information signal.
  • a utilization efficiency of the incident light L3 can be enhanced when a piece of information recorded on the thick type of optical disk 25 is reproduced, so that the output power of the incident light L3 can be minimized.
  • the recording of the information can be reliably performed without increasing the intensity of the incident light L3 because a transmission efficiency of the hologram lens 26, 32 or 33 for the incident light L3 is high. Also, in cases where a piece of information recorded on the high density optical disk 23 is reproduced in the photo detector 63, a signal-noise ratio of each signal obtained in the photo detector 63 can be enhanced because the transmission efficiency of the hologram lens 26, 32 or 33 for the light L3, L4R is high.
  • Fig. 43 is a constitutional view of an optical head apparatus according to a twelfth embodiment.
  • an optical head apparatus 111 for recording or reproducing pieces of information on or from the information medium 23 or 25, comprises the light source 52, the collimator lens 53, the beam splitter 54, the compound objective lens 29M (or 43, 45, 46 or 47) composed of the hologram lens 42 (or 26M or 32) and the objective lens 27, the actuating unit 58, the converging lens 55, the beam splitter 82, the photo detector 63, the wavefront changing device 56, and the photo detector 57.
  • a beam of incident light L3 radiated from the light source 52 is collimated in the collimator lens 53 and transmits through the beam splitter 54. Thereafter, a part of the incident light L3 transmits through the compound objective lens 29 without any diffraction, and a remaining part of the incident light L3 is diffracted.
  • the diffracted light L6 is converged on the first information medium 23 to form the converging spot S5. That is, the diffracted light L6 is incident on the rear surface of the first information medium 23, and the converging spot S5 is formed on the front surface of the first information medium 23. Thereafter, a beam of diffracted light L6R reflected at the front surface of the first information medium 23 passes through the same optical path in the reverse direction, and a great part of the diffracted light L6R is again diffracted by the hologram lens 42. Therefore, the diffracted light L6R transmits on the incoming optical path agreeing with the outgoing optical path.
  • the diffracted light L6R is reflected by the beam splitter 54 and is converged by the converging lens 55. Thereafter, a part of the diffracted light L6R transmits through the beam splitter 82. In this case, an astigmatic aberration is generated in the diffracted light L6R. Thereafter, the diffracted light L6R is converged on the photo detector 63 to form the converging spot S10 of which the shape is shown in Figs. 29A to 29C, and the intensity of the diffracted light L6R is detected in the photo detector 63. Therefore, an information signal and servo signals such as a focus error signal and a tracking error signal are obtained in the same manner as in the seventh embodiment.
  • the transmitted light L4 is converged on the second information medium 25 to form the converging spot S6. That is, the transmitted light L4 is incident on the rear surface of the second information medium 25, and the converging spot S6 is formed on the front surface of the second information medium 25. Thereafter, a beam of transmitted light L4R reflected at the front surface of the second information medium 25 passes through the same optical path in the reverse direction. That is, the transmitted light L4R is collimated by the objective lens 27 on the incoming optical path. Thereafter, a great part of the transmitted light L4R is diffracted by the hologram lens 42.
  • the transmitted light L4R transmits on the incoming optical path differing from the outgoing optical path. Thereafter, the transmitted light L4R is reflected by the beam splitter 54 and is converged by the converging lens 55. Thereafter, a part of the transmitted light L4R is reflected by the beam splitter 82. Thereafter, the wavefront of a great part of the transmitted light L4R is changed by the wavefront changing unit 56, and the great part of the transmitted light L4R is converged on the photo detector 57 to form converging spots S16, S17. Therefore, an information signal and servo signals such as a focus error signal and a tracking error signal are obtained in the same manner as in the sixth embodiment. Also, a remaining part of the transmitted light L4R not changed its wavefront by the wavefront changing unit 56 is converged on the photo detector 57 to form the converging spot S18.
  • the converging spot S18 formed on the photo detector 57 does not relate to a radiation point of the light source 52 in a mirror image, while the converging spot S10 formed on the photo detector 63 relates to the radiation point of the light source 52 in the mirror image.
  • a focal point of the transmitted light L4R converged by the converging lens 55 differs from that of the diffracted light L6R converged by the converging lens 55. Therefore, the photo detector 57 for detecting the intensity of the transmitted light L4R and the photo detector 63 for detecting the intensity of the diffracted light L6R are required.
  • the information can be reliably recorded or reproduced on or from the information medium regardless of whether the information medium is thick or thin.
  • the distance in an optical axis direction between the converging spots S5, S6 can be lengthened to about 1 mm. Therefore, even though the transmitted light L4 (or the diffracted light L6) is converged on the converging spot S6 (or S5) in focus to record or read a piece of information, the light L6 (or L4) is not converged on the converging spot S6 (or S5) in focus to reduce the intensity of the light L6 (or L4) at the converging spot S6 (or S5). Accordingly, no adverse influence is exerted on the recording or reproduction of the information
  • the hologram lens 42 functions as a convex lens for the first-order diffracted light L6, the occurrence of a chromatic aberration can be prevented in the optical head apparatus 111.
  • the diffraction efficiency of the hologram lens 26M or 42 in the compound objective lens 29M, 43, 45, 46 or 47 for changing a beam of light to a beam of first-order diffracted light is set to a value equal to or higher than 55 %.
  • a signal-noise ratio of each of the servo signals and the information signal obtained in the photo detector 57 can be enhanced because the transmitted light L4R diffracted by the hologram lens 26M or 42 at a high diffraction efficiency is utilized to obtain the servo signals and the information signal.
  • a utilization efficiency of the incident light L3 can be enhanced when a piece of information recorded on the thick type of optical disk 25 is reproduced, so that the output power of the incident light L3 can be minimized.
  • the recording of the information can be reliably performed without increasing the intensity of the incident light L3 because the diffraction efficiency of the hologram lens 26M or 42 for the incident light L3 and the diffracted light L6R is high. Also, in cases where a piece of information recorded on the high density optical disk 23 is reproduced in the photo detector 63, a signal-noise ratio of each signal obtained in the photo detector 63 can be enhanced because the diffraction efficiency of the hologram lens 26M or 42 for the light L3, L6R is high.
  • Fig. 44 is a constitutional view of an optical head apparatus according to a thirteenth embodiment.
  • an optical head apparatus 121 for recording or reproducing pieces of information on or from the information medium 23 or 25, comprises the light source 52, the collimator lens 53, the beam splitter 54, the compound objective lens 43 (or 29M, 45, 46 or 47) composed of the hologram lens 42 (or 26M or 32) and the objective lens 27, the actuating unit 58, the converging lens 55, the beam splitter 92 having the reflection type of hologram 93, the photo detector 63, and the photo detector 57.
  • the transmitted light L4 and the diffracted light L6 are converged by the converging lens 27 in the same manner as in the twelfth embodiment. Thereafter, in cases where a piece of information is recorded or reproduced on or from the first information medium 23, the diffracted light L6 is converged on the first information medium 23 to form the converging spot S5. Thereafter, a beam of diffracted light L6R reflected by the first information medium 23 passes through the same optical path in the reverse direction, and a large part of the diffracted light L6R is diffracted by the hologram lens 42. Therefore, the diffracted light L6R transmits on the incoming optical path agreeing with the outgoing optical path in the same manner as in the twelfth embodiment.
  • the diffracted light L6R is reflected by the beam splitter 54 and is converged by the converging lens 55 on the beam splitter 92 to form a converging spot on the reflection type of hologram 93 of the beam splitter 92. Therefore, all of the diffracted light L6R is diffracted and reflected by the hologram 93 to be converged on the photo detector 57 in the same manner as in the tenth embodiment. Therefore, an information signal and servo signals such as a focus error signal and a tracking error signal are obtained in the same manner as in the sixth embodiment.
  • the transmitted light L4 is converged on the second information medium 25 to form the converging spot S6. Thereafter, a beam of transmitted light L4R reflected by the second information medium 25 passes through the same optical path in the reverse direction. That is, a large part of the transmitted light L4R is collimated by the objective lens 27 on the incoming optical path. Thereafter, a great part of the transmitted light L4R is diffracted by the hologram lens 42. Therefore, the transmitted light L4R transmits on the incoming optical path differing from the outgoing optical path in the same manner as in the twelfth embodiment.
  • the transmitted light L4R is reflected by the beam splitter 54 and is converged by the converging lens 55. Thereafter, a large part of the transmitted light L4R transmits through the beam splitter 92. In this case, an astigmatic aberration is generated in the transmitted light L4R. Thereafter, the transmitted light L4R is converged on the photo detector 63 to form a converging spot S19 of which the shape is the same as the converging spot S10 shown in Figs. 29A to 29C, and the intensity of the transmitted light L4R is detected in the photo detector 63. Therefore, an information signal and servo signals such as a focus error signal and a tracking error signal are obtained in the same manner as in the seventh embodiment.
  • the converging spot S19 formed on the photo detector 63 does not relate to a radiation point of the light source 52 in a mirror image. Therefore, the photo detector 57 for detecting the intensity of the diffracted light L6R and the photo detector 63 for detecting the intensity of the transmitted light L4R are required.
  • the compound objective lens having two focal points is utilized in the optical head apparatus 121, pieces of information can be reliably recorded or reproduced on or from an information medium regardless of whether the information medium is thick or thin.
  • the distance in an optical axis direction between the converging spots S5, S6 can be lengthened to about 1 mm. Therefore, even though the transmitted light L4 (or the diffracted light L6) is converged on the converging spot S6 (or S5) in focus to record or read a piece of information, the light L6 (or L4) is not converged on the converging spot S6 (or S5) in focus to reduce the intensity of the light L6 (or L4) at the converging spot S6 (or S5). Accordingly, no adverse influence is exerted on the recording or reproduction of the information
  • the hologram lens 42 functions as a convex lens for the first-order diffracted light L6, the occurrence of a chromatic aberration can be prevented in the optical head apparatus 121.
  • the diffraction efficiency of the hologram lens 26M or 42 in the compound objective lens 29M, 43, 45, 46 or 47 for changing a beam of light to a beam of first-order diffracted light is set to a value equal to or higher than 70 %.
  • a signal-noise ratio of each of the servo signals and the information signal obtained in the photo detector 57 can be enhanced because the transmitted light L4R diffracted by the hologram lens 26M or 42 at a high diffraction efficiency is utilized to obtain the servo signals and the information signal.
  • a utilization efficiency of the incident light L3 can be enhanced when a piece of information recorded on the thick type of optical disk 25 is reproduced, so that the output power of the incident light L3 can be minimized.
  • the recording of the information can be reliably performed without increasing the intensity of the incident light L3 because the diffraction efficiency of the hologram lens 26M or 42 for the incident light L3 and the diffracted light L6R is high. Also, in cases where a piece of information recorded on the high density optical disk 23 is reproduced in the photo detector 63, a signal-noise ratio of each signal obtained in the photo detector 63 can be enhanced because the diffraction efficiency of the hologram lens 26M or 42 for the light L3, L6R is high.
  • Fig. 45 is a constitutional view of an optical head apparatus according to a fourteenth embodiment.
  • Fig. 46 is a plan view of a hologram lens utilized in the optical head apparatus shown in Fig. 45.
  • an optical head apparatus 131 for recording or reproducing pieces of information on or from the information medium 23 or 25, comprises the light source 52, a beam splitter 132 having a polarizing separation film 133 on its surface for reflecting the incident light L3 radiated from the light source 52 on an outgoing optical path and transmitting through the light L4R or L5R reflected on the information medium 23 or 25 on an incoming optical path, a collimator lens 134 for collimating the incident light L3 on the outgoing optical path and converging the light L4R or L5R on the incoming optical path, a hologram lens 135 for transmitting a part of the incident light L3 without any diffraction and diffracting a remaining part of the incident light L3, the 1/4- ⁇ plate 69, the objective lens 27, the actuating unit 58, and a photo detector 136 for detecting the light transmitting through or diffracted by the hologram lens 135 on the incoming optical path.
  • the hologram lens 135 is formed by drawing the grating pattern P1 in a central region 135a of the transparent substrate 28 and a grating pattern P12 in a peripheral region 135b surrounding the central region 135a.
  • the grating pattern P12 is drawn in a non-concentric shape.
  • a compound objective lens 137 having two focal points is composed of the hologram lens 135 and the objective lens 27.
  • Light passing through the peripheral region 135b of the hologram lens 135 is detected by the photo detector 136 to cancel noises included in an information signal.
  • An optical axis of the optical head apparatus 131 passes through a central point of the grating pattern P1 and a central axis of the objective lens 27.
  • the photo detector 136 comprises the quadrant photo-detector 64 having the detecting sections SE7 to SE10 and a noise cancelling photo detector 138 for detecting the intensity of light passing through the peripheral region 135b of the hologram lens 135. Because the grating pattern P12 of the peripheral region 135b is drawn in the non-concentric shape, light diffracted in the peripheral region 135b is not converged on the detecting sections SE7 to SE10.
  • the incident light L3 linearly polarized in a first direction is radiated from the light source 52 and is reflected by the beam splitter 132 because the polarizing separation film 133 functions as a mirror for the incident light L3 linearly polarized in the first direction. Therefore, the incident light L3 is directed in an upper direction and is collimated by the collimator lens 134.
  • a part of the incident light L3 incident on the central region 135a of the hologram lens 135 transmits through the central region 135a without any diffraction to form the transmitted light L4, and a remaining part of the incident light L3 incident on the central region 135a of the hologram lens 135 is diffracted in the central region 135a to form the diffracted light L5.
  • a part of the incident light L3 incident on the peripheral region 135b of the hologram lens 135 transmits through the peripheral region 135b without any diffraction to form a beam of noise cancelling light L14.
  • the light L4, L5 and L14 pass through the 1/4- ⁇ plates so that the light L4, L5 and L14 linearly polarized in the first direction is changed to the light L4, L5 and L14 circularly polarized. Thereafter, the light L4, L5 and L14 are converged by the converging lens 27.
  • the transmitted light L4 (or the diffracted light L5) is converged on the information medium 23 (or 25) to form the converging spot S1 (or S2).
  • a beam of transmitted light L4R (or a beam of diffracted light L5R) reflected by the information medium 23 (or 25) passes through the same optical path in the reverse direction. That is, the transmitted light L4R (or the diffracted light L5R) is circularly polarized in reverse and again passes through the converging lens 27 and the 1/4- ⁇ plate 69.
  • the light L4R (or L5R) is linearly polarized in a second direction perpendicular to the first direction. Thereafter, a part of the transmitted light L4R transmits through the central region 135a of the hologram lens 135 without any diffraction, or a part of the diffracted light L5R is again diffracted in the central region 135a. Thereafter, the transmitted light L4R (or the diffracted light L5R) is converged by the collimator lens 134 and passes through the beam splitter 132 without any reflection because the polarizing separation film 133 functions as a transparent plate for the light L4R (or L5R) linearly polarized in the second direction.
  • an astigmatic aberration is generated in the transmitted light L4R (or the diffracted light L5R) in the same manner as in the seventh embodiment.
  • the transmitted light L4R (or the diffracted light L5R) is incident on the detecting sections SE7 to SE10 of the photo detector 136 to form a converging spot S20 of which the shape is the same as the converging spot S10 shown in Figs. 29A to 29C.
  • the intensity of the transmitted light L4R (or the diffracted light L5R) is changed to electric current signals SC21 to SC24 in the detecting sections SE7 to SE10.
  • servo signals such as a focus error signal and a tracking error signal are obtained in the same manner as in the seventh embodiment, so that the position of the compound objective lens 137 is adjusted to converge the transmitted light L4 (or the diffracted light L5) on the information medium 23 (or 25) in focus.
  • the noise cancelling light L14 is converged on the information medium 23 to form a converging spot surrounding the converging spot S1. Thereafter, a beam of noise cancelling light L14R reflected by the first information medium 23 passes through the same optical path in the reverse direction. That is, the noise cancelling light L14R again passes through the converging lens 27 and the 1/4- ⁇ plate 69, and a part of the noise cancelling light L14R is diffracted and converged in the peripheral region 135b of the hologram lens 135 and is incident on the noise cancelling photo detector 138. In the photo detector 138, an output signal SC25 is generated according to the intensity of the noise cancelling light L14R.
  • signals expressing pieces of information recorded on an optical disk shifts to a higher frequency as the density of the information recorded becomes high.
  • the amplitude of a signal having a high frequency becomes low as compared with that of a signal having a low frequency in cases where the signals are produced according to light passing through a central region of a hologram lens.
  • the amplitude of a signal having a high frequency is emphasized in cases where the signal is produced according to light passing through a peripheral region of the hologram lens.
  • the compound objective lens having two focal points is utilized in the optical head apparatus 131, pieces of information can be reliably recorded or reproduced or or from an information medium regardless of whether the information medium is thick or thin.
  • the information signal S nc can be reliably reproduced at a high signal-noise ratio.
  • the intensity of the light L4R or L5R incident on the detecting sections SE7 to SE10 of the photo detector 136 is reduced by converging the noise cancelling light L14R on the photo detector 138, a positioning accuracy of the photo detector 136 can be coarsely lowered to 1/100.
  • Fig. 47 is a constitutional view of an optical head apparatus according to a fifteenth embodiment.
  • Fig. 48 is a plan view of a hologram lens utilized in the optical head apparatus shown in Fig. 47.
  • an optical head apparatus 141 for recording or reproducing pieces of information on or from the information medium 23 or 25, comprises the light source 52, the beam splitter 82, the collimator lens 134, a hologram lens 142 for transmitting a part of the incident light L3 without any diffraction and diffracting a remaining part of the incident light L3, the objective lens 27, the actuating unit 58, and a photo detector 143 for detecting the light transmitting through or diffracted by the hologram lens 142 on the incoming optical path.
  • the hologram lens 142 is partitioned into a central region 142a in which the grating pattern P1 is drawn, a pair of side peripheral regions 142b, 142c in which grating patterns P13, P14 are drawn to cancel noises included in an information signal, and a pair of no-designed regions 142d, 142e in which no grating pattern is drawn not to reduce the intensity of light. Because the grating pattern P1 are drawn in the hologram lens 135, a compound objective lens 144 having two focal points is composed of the hologram lens 142 and the objective lens 27. An optical axis of the optical head apparatus 141 passes through a central point of the grating pattern P1 and a central axis of the objective lens 27.
  • the photo detector 143 comprises the quadrant photo-detector 64 having the detecting sections SE7 to SE10, a pair of noise cancelling photo detector 138a, 138b for detecting the intensity of light passing through the peripheral region 142b, 142c of the hologram lens 142.
  • the transmitted light L4 (or the diffracted light L5) generated in the central region 142a of the hologram lens 142 is converged on the first information medium 23 (or the second information medium 25) in an outgoing optical path to form the converging spot S1 (or S2).
  • the transmitted light L4R (or the diffracted light L5R) passes through the same optical path in the reverse direction. That is, the transmitted light L4R (or the diffracted light L5R) again passes through the converging lens 27, and a part of the transmitted light L4R transmits through the central region 142a of the hologram lens 142 without any diffraction or a part of the diffracted light L5R is again diffracted in the central region 142a.
  • the transmitted light L4R (or the diffracted light L5R) is converged by the collimator lens 134 and passes through the beam splitter 82.
  • an astigmatic aberration is generated in the transmitted light L4R (or the diffracted light L5R) in the same manner as in the seventh embodiment.
  • the transmitted light L4R (or the diffracted light L5R) is incident on the detecting sections SE7 to SE10 of the photo detector 143 to form a converging spot S21 of which the shape is the same as the converging spot S10 shown in Figs. 29A to 29C.
  • a part of the incident light L3 incident on the peripheral region 142b of the hologram lens 142 transmits through the peripheral region 142b without any diffraction to form a beam of noise cancelling light L15
  • a part of the incident light L3 incident on the peripheral region 142c of the hologram lens 142 transmits through the peripheral region 142c without any diffraction to form a beam of noise cancelling light L16.
  • the noise cancelling light L15, L16 are converged on the information medium 23 to form a converging spot surrounding the converging spot S1.
  • beams of noise cancelling light L15R, L16R reflected by the first information medium 23 passes through the same optical path in the reverse direction.
  • the noise cancelling light L15R, L16R again passes through the converging lens 27.
  • a part of the noise cancelling light L15R is diffracted and converged in the peripheral region 142b of the hologram lens 142 and is incident on the noise cancelling photo detector 138a
  • a part of the noise cancelling light L16R is diffracted and converged in the peripheral region 142c of the hologram lens 142 and is incident on the noise cancelling photo detector 138b.
  • an output signal SC30 is generated according to the intensity of the noise cancelling light L15R.
  • an output signal SC31 is generated according to the intensity of the noise cancelling light L16R in the photo detector 138b.
  • the compound objective lens having two focal points is utilized in the optical head apparatus 141, pieces of information can be reliably recorded or reproduced from an information medium regardless of whether the information medium is thick or thin.
  • a signal-noise ratio in the information signal S nc can be enhanced in the same manner as in the fourteenth embodiment.
  • the information signal S nc can be reliably reproduced at a high signal-noise ratio.
  • the intensity of the light L4R or L5R incident on the detecting sections SE7 to SE10 of the photo detector 143 is reduced by converging the noise cancelling light L15R, L16R on the photo detectors 138a, 138b, a positioning accuracy of the photo detector 143 can be coarsely lowered to 1/100.
  • the size of the converging spot of the unnecessary diffracted light formed in defocus on the first information medium 23 becomes larger than that in the fourteenth embodiment.
  • more pieces of information recorded on the first information medium 23 are read by the unnecessary diffracted light, and the information are treated as a piece of averaged information in the photo detector 143 even though the unnecessary diffracted light is incident on the photo detector 143.
  • the information read by the unnecessary diffracted light is moreover averaged, and the averaged information does not adversely influence on the information signal S nc as a noise.
  • the unnecessary diffracted light can be prevented from being incident on the photo detector 64 in which each of the detecting sections SE7 to SE10 has SL0 square in size.
  • the light Lu 1 is converged on a first position PT1 spaced SP1 (SP1 > SL0) from the center of the photo detector 64.
  • a far field pattern of the incident light L3 incident on the hologram lens 142 is distributed in the Gaussian distribution as shown in Fig. 13A, and a cross-sectional beam profile of the incident light L3 distributed in the Gaussian distribution is in an elliptic shape. That is, a beam divergent angle (or a full angle at half maximum) of the incident light L3 in a perpendicular direction is larger than that in a horizontal direction.
  • the perpendicular direction of the incident light L3 is directed in an X2 direction shown in Fig. 48
  • the horizontal direction of the incident light L3 is directed in a Y2 direction shown in Fig. 48.
  • the intensity of the incident light L3 transmitting through the hologram lens 142 without any diffraction is largely reduced in the perpendicular direction as compared with that in the horizontal direction. Therefore, the cross-sectional beam profile of the incident light L3 is corrected to a circular shape in the hologram lens 142. That is, the converging spot S1 formed on the first information medium 23 is corrected to the circular shape. Accordingly, secondary maxima (or side lobes) occurring around the converging spot S1 can be lowered, and a signal-noise ratio of the information signal S nc can be enhanced.
  • the noise cancelled information signal S nc is obtained according to the equation (15).
  • the noises included in the information can be moreover reduced.
  • Fig. 50 is a constitutional view of an optical head apparatus according to a sixteenth embodiment.
  • Fig. 51 is a diagonal view of a light source and photo detectors utilized in the optical head apparatus shown in Fig. 50.
  • an optical head apparatus 151 for recording or reproducing pieces of information on or from the information medium 23 or 25, comprises the light source 52 for radiating the incident light L3 linearly polarized in a non-diffracting direction parallel to an X3 axis, an holographic element 152 for transmitting through the incident light L3 without any diffraction on an outgoing optical path and diffracting the transmitted light L4R or the diffracted light L5R linearly polarized in a diffracting direction parallel to a Y3 axis on an incoming optical path, the collimator lens 53, the 1/4- ⁇ plate 69, the hologram lens 26 (or 26M, 32, 33, 42. 135 or 142), the objective lens 27, the actuating unit 58, and a photo detector 153 for detecting the intensity of the light L4R or L5R diffracted by the holographic element 152.
  • the light source 52 and the photo detector 153 are located on a substrate 154 to precisely fix a relative position between the light source 52 and the photo detector 153.
  • the photo detector 153 comprises the sextant photo-detector 59 having the detecting sections SE1 to SE6 and the tracking photo-detectors 60a to 60d.
  • a mirror element 155 is located on the substrate 154 to direct the incident light L3 radiated from the light source 52 in a Z3 direction.
  • the holographic element 152 is produced by proton-exchanging surface parts of a lithium niobate substrate or by utilizing a liquid crystal cell, as is described in Provisional Publication No. 189504/86 (S61-189504) and Provisional Publication No. 241735/88 (S63-241735). Therefore, light linearly polarized in a non-diffracting direction parallel to an X3 axis transmits through the holographic element 152 without any diffraction. In contrast, light linearly polarized in a diffracting direction parallel to a Y3 axis which is perpendicular to the X3 axis is diffracted by the holographic element 152.
  • the incident light L3 linearly polarized in a non-diffracting direction parallel to an X3 axis is radiated from the light source 52 and transmits through the holographic element 152 without any diffraction. Thereafter, the incident light L3 is collimated by the collimator lens 53, and the incident light L3 linearly polarized is changed to the incident light L3 circularly polarized by the 1/4- ⁇ plate 69. Thereafter, a part of the incident light L3 transmits through the hologram lens 26 without any diffraction to form the transmitted light L4, and a remaining part of the incident light L3 is diffracted by the hologram lens 26 to form the diffracted light L5.
  • the light L4, L5 are converged by the objective lens 27, and the converging spot S1 of the transmitted light L4 (or the converging spot S2 of the diffracted light L5) is formed on the first information medium 23 (or the second information medium 25).
  • the light L4 or L5 is reflected by the information medium 23 (or 25) and is changed to the light L4R (or L5R)
  • a rotational direction of the circular polarization in the light L4 is reversed. Therefore, the light L4R (or L5R) having the reversed circular polarization passes through the same optical path in the opposite direction.
  • the transmitted light L4R (or the diffracted light L5R) again passes through the converging lens 27, and a part of the transmitted light L4R transmits through the hologram lens 142 without any diffraction or a part of the diffracted light L5R is again diffracted by the hologram lens 142. Thereafter, the transmitted light L4R (or the diffracted light L5R) circularly polarized in reverse is changed to the light L4R (or L5R) linearly polarized in a diffracting direction parallel to a Y3 axis by the 1/4- ⁇ plate 69.
  • the light L4R (or L5R) is converged by the collimator lens 53 and is diffracted by the holographic element 152 to form a plurality of converging spots on the photo detectors 153. Therefore, an information signal expressing a piece of information recorded on the information medium 23 (or 25) and servo signals such as a focus error signal and a tracking error signal are obtained in the photo detector 153 in the same manner as in the sixth embodiment.
  • the compound objective lens having two focal points is utilized in the optical head apparatus 151, pieces of information can be reliably recorded or reproduced or or from an information medium regardless of whether the information medium is thick or thin.
  • the incident light L3 transmits through the holographic element 152 on the outgoing optical path and because all of the light L4R or L5R is diffracted by the holographic element 152 on the incoming optical path, a utilization efficiency of the incident light L3 can be enhanced. Therefore, even though a radiation intensity of the incident light L3 in the light source 52 is low, the information signal and the servo signals having a high signal-noise ratio can be reliably obtained.
  • the optical head apparatus 151 can be manufactured at a small size, in a light weight, and at a low cost.
  • optical head apparatus 151 because optical parts of the optical head apparatus 151 are located along its optical axis, the optical head apparatus 151 stably operated can be obtained even though a circumstance temperature largely varies and the apparatus is operated for a long time.
  • a diffraction efficiency of the holographic element 152 be heightened to set a transmission efficiency of the holographic element 152 to almost zero.
  • a combination of the holographic element 152 and the 1/4- ⁇ plate 69 function functions as an isolator to prevent the light L4R or L5R from returning to the light source 52. Therefore, in cases where a semiconductor laser is utilized as the light source 52, any light does not return to an active layer of the semiconductor laser. Accordingly, noises induced by the light returning to the semiconductor laser can be prevented.
  • the light source 52 and the photo detector 153 are located on the same substrate 154, the light source 52 and the photo detector 153 can be closely arranged each other. Therefore, a relative position between the light source 52 and the photo detector 153 can be easily set at a high accuracy. For example, the relative position can be set at an accuracy within several ⁇ m. Accordingly, a manufacturing cost of the optical head apparatus 151 can be lowered, and the optical head apparatus 151 can be moreover manufactured at a small size, in a light weight, and at a low cost.
  • the light source 52 is electrically connected with an external circuit through first wirings
  • the photo detector 153 is electrically connected with another external circuit through second wirings.
  • the first and second wirings can pass on an X3-Y3 plane in common. Therefore, the light source 52 and the photo detector 153 can be easily and automatically connected with the external circuits.
  • reference lines required to connect the light source 52 and the photo detector 153 with the external circuits are only drawn on the X3-Y3 plane, the relative position between the light source 52 and the photo detector 153 can be easily set at a high accuracy.
  • the optical head apparatus 151 with the holographic element 152 is described. However, in cases where the intensity of the incident light L3 is sufficient, it is applicable that a hologram having a small grating pitch or a blazed hologram be utilized in place of the holographic element 152. In this case, pieces of information can be reliably recorded or reproduced on or from an information medium regardless of whether the information medium is thick or thin. Also, because no beam splitter is utilized in the optical head apparatus 151, the optical head apparatus 151 can be manufactured at a small size, in a light weight, and at a low cost. Also, because optical parts of the optical head apparatus 151 are located along its optical axis, the optical head apparatus 151 stably operated can be obtained even though a circumstance temperature largely varies and the apparatus is operated for a long time.
  • Fig. 52 is a constitutional view of an optical head apparatus according to a seventeenth embodiment.
  • an optical head apparatus 161 for recording or reproducing pieces of information on or from the information medium 23 or 25, comprises the light source 52 for radiating the incident light L3 linearly polarized in a first direction, the collimator lens 53, a polarizing separation film 162 formed on a front surface of a transparent substrate 162 for reflecting the incident light L3 linearly polarized in the first direction and transmitting light linearly polarized in a second direction perpendicular to the first direction, the 1/4- ⁇ plate 69, the hologram lens 26 (or 26M, 32, 33, 42, 135 or 142), the objective lens 27, the actuating unit 58, a reflection-type hologram 164 formed on a rear surface of the transparent substrate 162 for diffracting and reflecting the light L4R, L5R, and the photo detector 57.
  • the incident light L3 linearly polarized in a first direction is radiated from the light source 52 and is collimated by the collimator lens 53. Thereafter, all of the incident light L3 is reflected by the polarizing separation film 162 because the incident light L3 is linearly polarized in the first direction. Therefore, the incident light L3 is directed in an upper direction. Thereafter, the linear polarization of the incident light L3 is changed to a circular polarization in the 1/4- ⁇ plate 69, and a part of the incident light L3 transmits through the hologram lens 26 to form the transmitted light L4. Also, a remaining part of the incident light L3 is diffracted by the hologram lens 26 to form the diffracted light L5.
  • the light L4, L5 are converged by the objective lens 27, and the converging spot S1 of the transmitted light L4 (or the converging spot S2 of the diffracted light L5) is formed on the first information medium 23 (or the second information medium 25).
  • the transmitted light L4R (or the diffracted light L5R) circularly polarized in reverse again passes through the converging lens 27 in the same manner as in the sixteenth embodiment, and a part of the transmitted light L4R transmits through the hologram lens 26 without any diffraction or a part of the diffracted light L5R is again diffracted by the hologram lens 26.
  • the transmitted light L4R (or the diffracted light L5R) circularly polarized in reverse is changed to the light L4R (or L5R) linearly polarized in a second direction perpendicular to the first direction by the 1/4- ⁇ plate 69.
  • all of the light L4R (or L5R) is refracted by the polarizing separation film 162 and is diffracted and reflected by the hologram 164.
  • the light L4R (or L5R) transmits through the polarizing separation film 162 and is converged by the collimator lens 53 to form a plurality of converging spots on the photo detector 57. Therefore, an information signal expressing a piece of information recorded on the information medium 23 (or 25) and servo signals such as a focus error signal and a tracking error signal are obtained in the photo detector 57 in the same manner as in the sixth embodiment.
  • the compound objective lens having two focal points is utilized in the optical head apparatus 161
  • pieces of information can be reliably recorded or reproduced on or from an information medium regardless of whether the information medium is thick or thin.
  • the incident light L3 incident on the polarizing separation film 162 is collimated, a reflectivity for the incident light L3 is uniform over the entire film 162. Therefore, a diffraction-limited spot of the light L4 or L5 can be easily formed on the information medium 23 or 25. Also, because the light L4R, L5R incident on the polarizing separation film 162 are collimated, a transmissivity for the light L4R, L5R is uniform over the entire film 162. Therefore, an offset occurring in the servo signals can be prevented.
  • the incident light L3 transmits through the hologram 164 on the outgoing optical path and because all of the light L4R or L5R is diffracted by the hologram 164 on the incoming optical path, a utilization efficiency of the incident light L3 can be enhanced. Therefore, even though a radiation intensity of the incident light L3 in the light source 52 is low, the information signal and the servo signals having a high signal-noise ratio can be reliably obtained.
  • the optical head apparatus 161 can be manufactured at a small size, in a light weight, and at a low cost.
  • optical head apparatus 161 because optical parts of the optical head apparatus 161 are located along its optical axis, the optical head apparatus 161 stably operated can be obtained even though a circumstance temperature largely varies and the apparatus is operated for a long time.
  • a combination of the film 162 and the 1/4- ⁇ plate 69 function functions as an isolator to prevent the light L4R or L5R from returning to the light source 52. Therefore, in cases where a semiconductor laser is utilized as the light source 52, any light does not return to an active layer of the semiconductor laser. Accordingly, noises induced by the light returning to the semiconductor laser can be prevented.
  • the hologram 164 be blazed. In this case, because the generation of unnecessary diffracted light such as minus first-order diffracted light in the hologram 164 is prevented, a diffraction efficiency of the hologram 164 for changing light to first-order diffracted light can be set to almost 100%. Therefore, the incident light L3 can be efficiently utilized to obtain the signals.
  • the servo signals can be stably obtained.
  • the collimator lens 53 is located between the light source 52 and the film 162. However, the collimator lens 53 is not necessary in the optical head apparatus 161.
  • the optical head apparatus 161 with the film 162 and the 1/4- ⁇ plate 69 is described. However, in cases where the intensity of the incident light L3 is sufficient, it is applicable that a reflection film having a reflectivity of almost 1/3 be utilized in place of the film 162 and the 1/4- ⁇ plate 69 be omitted. In this case, pieces of information can be reliably recorded or reproduced on or from an information medium regardless of whether the information medium is thick or thin. Also, because a hybrid element composed of the film 162, the substrate 163 and the hologram 164 functions as a beam splitter and a rising mirror, the optical head apparatus 161 can be manufactured at a small size, in a light weight, and at a low cost. Also, because optical parts of the optical head apparatus 161 are located along its optical axis, the optical head apparatus 161 stably operated can be obtained even though a circumstance temperature largely varies and the apparatus is operated for a long time.
  • pieces of information can be reliably recorded or reproduced on or from an information medium regardless of whether the information medium represents a conventional optical disk such as a compact disk having a thickness T2 of about 1.2mm or a prospective high density optical disk having a thickness T1 ranging from 0.4mm to 0.8mm.
  • the information recorded or reproduced on or from the information medium it is required to examine the thickness of the information medium in advance. Therefore, in cases where a piece of distinguishing information is recorded on the information medium in advance to distinguish the thickness of the information medium, it is convenient for a user. Because no distinguishing information is recorded on the conventional optical disk, it is preferred that the distinguishing information be recorded on the prospective high density optical disk appearing on the market in the future. Therefore, first and second high density optical disks with the distinguishing information are described below.
  • Fig. 53 is a diagonal view of a first high density optical disk, a cross sectional view of the disk being partially shown.
  • a high density optical disk 171 is partitioned into an outer region 171a and an inner region 171b.
  • the outer region 171a occupies a large part of the optical disk 171, and an information recording substrate 171c of the outer region 171a has the thickness T1, and the information recording substrate 171c of the inner region 171b has the thickness T2.
  • a plurality of first recording pits 172 are formed on the information recording substrate 171c of the outer region 171a at narrow intervals in series to record pieces of information at a high density.
  • a plurality of second recording pits 173 are formed on the information recording substrate 171c of the inner region 171b at ordinary intervals in series to record pieces of distinguishing information at an ordinary density of a compact disk.
  • the distinguishing information inform that the optical disk 171 has the thickness T1.
  • the thickness T1 of the outer region 171a for example, ranges from 0.4mm to 0.8mm, and the thickness T2 of the inner region is, for example, about 1.2mm.
  • the diffracted light L5 according to the first or second embodiment (or the transmitted light L4 according to the third embodiment) is initially converged on an inner region of the information medium 23, 25 while performing a focus control corresponding to the second information medium 25 having the thickness T2.
  • the information medium 23 or 25 is the optical disk 171
  • a piece of distinguishing information informing that the optical disk 171 having the thickness T1 is converged by the light L5 (or L4) is detected.
  • the transmitted light L4 (or the diffracted light L6) is automatically converged on the outer region 171a of the optical disk 171 while performing a focus control corresponding to the first information medium 23 having the thickness T1.
  • the information medium 23 or 25 is a thick type of conventional optical disk having a thickness T2
  • no distinguishing information is detected when the light L5 (or L4) is converged on the inner region 171b of the conventional optical disk.
  • the focus control corresponding to the second information medium 25 is continued to detect an information signal expressing a piece of information recorded on the conventional optical disk.
  • pieces of information can be automatically recorded or reproduced on or from an information medium regardless of whether the information medium is thin or thick.
  • the inner region can be small. Therefore, a memory capacity of the optical disk 171 is not lowered by the addition of the second recording pit 173.
  • Fig. 54 is a diagonal view of a second high density optical disk, a cross sectional view of the disk being partially shown.
  • a high density optical disk 174 is partitioned into an outer region 174a and an inner region 174b.
  • the outer region 174a occupies a large part of the optical disk 174.
  • the optical disk 174 has a uniform thickness of T1.
  • the first recording pits 172 are formed on an information recording substrate 174c of the outer region 174a to record pieces of information at a high density.
  • a plurality of second recording pits 175 having a large size are formed on the information recording substrate 174c of the inner region 174b at wide intervals to record pieces of distinguishing information at a lower density than the ordinary density.
  • the distinguishing information inform that the entire optical disk 174 has the thickness T1.
  • the thickness T1 of the optical disk 174 for example, ranges from 0.4mm to 0.8mm.
  • the diffracted light L5 according to the first or second embodiment (or the transmitted light L4 according to the third embodiment) is initially converged on an inner region of the information medium 23 or 25 while performing a focus control corresponding to the second information medium 25 having the thickness T2.
  • the information medium 23 or 25 is the optical disk 174
  • the light L5 (or L4) is converged on each of the second recording pits 175 in defocus.
  • a converging spot of the light L5 (or L4) is reliably formed in one of the second recording pits 175.
  • the information medium 23 or 25 is a thick type of conventional optical disk having a thickness T2
  • no distinguishing information is detected when the light L5 (or L4) is converged on the inner region 174b of the conventional optical disk.
  • the focus control corresponding to the second information medium 25 is continued to detect an information signal expressing a piece of information recorded on the conventional optical disk.
  • pieces of information can be automatically recorded or reproduced on or from an information medium regardless of whether the information medium is thin or thick.
  • the inner region of the optical disk 174 can be small. Therefore, a memory capacity of the optical disk 174 is not lowered by the addition of the second recording pit 173.
  • the thickness of the optical disk 174 is uniform, the optical disk 174 can be easily manufactured at a low cost. Also, the optical disk 174 can be thinned.
  • An optical disk apparatus with one of the optical head apparatuses in which it is automatically judged whether a high density optical disk having the thickness T1 or a conventional optical disk having the thickness T2 is utilized is described.
  • Fig. 55 is a block diagram of an optical disk apparatus with one of the optical head apparatuses shown in Figs. 21, 27, 30, 31, 32, 33, 37, 38, 40A, 43, 44, 50 and 52 according to a eighteenth embodiment.
  • Fig. 56 is a flow chart showing the operation of the optical disk apparatus shown in Fig. 55.
  • an optical disk apparatus 176 for recording or reproducing pieces of information on or from the high density optical disk 171 (or 174) or the conventional optical disk 25 comprises the optical head apparatus 51 (or 61, 65, 67, 70, 71, 81, 91, 101, 111, 121, 151 or 161), a moving means 177 such as a feed mechanism for moving the optical head apparatus 51 to a prescribed position, and a rotating means 178 such as a spindle motor for rotating the high density optical disk 171 (or 174) or the conventional optical disk 25.
  • the high density optical disk 171 or the conventional optical disk 25 is set to a prescribed position of the optical disk apparatus 176, and the optical disk 171 or 25 is rotated by the rotating means 178. Thereafter, the optical head apparatus 51 is moved to a position just under an innermost recording track of the optical disk 171 or 25 in a step 211, and the diffracted light L5 is converged on the innermost recording track of the optical disk 171 or 25 while performing a focus control corresponding to the conventional optical disk 25 of the thickness T2 in a step 212. Thereafter, a tracking control is performed, and a piece of information recorded on the innermost recording track of the optical disk 171 or 25 is detected in a step 213. Thereafter, it is judged in a step 214 whether the information agrees with a piece of distinguishing information informing that the optical disk 171 having the thickness T1 is set to the optical disk apparatus 176.
  • the distinguishing information is detected. Thereafter, the transmitted light L4 is automatically converged on the optical disk 171 while performing a focus control corresponding to the optical disk 171 of the thickness T1 in a step 215. Therefore, pieces of information are recorded or reproduced on or from the optical disk 171.
  • the conventional optical head 25 is set to the optical disk apparatus 176, the distinguishing information is not detected. In this case, the convergence of the diffracted light L5 on the conventional optical disk 25 is continued while performing the focus control and the tracking control corresponding to the conventional optical disk 25 in a step 216. Therefore, pieces of information are recorded or reproduced on or from the conventional optical disk 25.
  • the thickness of the optical disk set in the optical disk apparatus 176 can be rapidly judged at a high accuracy. Also, pieces of information can be stably recorded or reproduced on or from an optical disk regardless of whether the optical disk is the high density optical disk 171 (or 174) or the conventional optical disk 25.
  • An optical disk apparatus with one of the optical head apparatuses in which it is automatically judged whether a high density optical disk having the thickness T1 or a conventional optical disk having the thickness T2 is utilized is described.
  • Fig. 57 is a block diagram of an optical disk apparatus with one of the optical head apparatuses shown in Figs. 21, 27, 30, 31, 32, 33, 37, 38, 40A, 43, 44, 50 and 52 according to a nineteenth embodiment.
  • Fig. 58 is a flow chart showing the operation of the optical disk apparatus shown in Fig. 57.
  • an optical disk apparatus 176 for recording or reproducing pieces of information on or from a high density optical disk 182 or the conventional optical disk 25 comprises the optical head apparatus 51 (or 61, 65, 67, 70, 71, 81, 91, 101, 111, 121, 151 or 161), the moving means 177, and a rotating means 182 such as a spindle motor for rotating the high density optical disk 182 or the conventional optical disk 25.
  • the high density optical disk 182 has no distinguishing information and has the thickness T1.
  • the high density optical disk 182 or the conventional optical disk 25 is set to a prescribed position of the optical disk apparatus 181, and the optical disk 182 or 25 is rotated by the rotating means 182. Thereafter, the optical head apparatus 51 is moved to a position just under an innermost recording track of the optical disk 182 or 25 in a step 221 because a piece of information is reliably recorded on the innermost recording track, and the diffracted light L5 is converged on the innermost recording track of the optical disk 182 or 25 while performing a focus control corresponding to the conventional optical disk 25 of the thickness T2 in a step 222. Thereafter, a tracking control is performed, and a piece of information recorded on the innermost recording track of the optical disk 182 or 25 is detected in a step 223.
  • the intensity of an information signal expressing the information detected is more than a threshold value. That is, the intensity of the information signal more than the threshold value denotes that the diffracted light L5 is converged in focus on the optical disk 182 or 25, and the intensity of the information signal not more than the threshold value denotes that the diffracted light L5 is converged in defocus on the optical disk 182 or 25.
  • the intensity of the information signal not more than the threshold value is detected.
  • the transmitted light L4 is automatically converged on the optical disk 182 while performing a focus control corresponding to the high density optical disk 182 of the thickness T1 in a step 225. Therefore, pieces of information are recorded or reproduced on or from the optical disk 182.
  • the conventional optical head 25 is set to the optical disk apparatus 181
  • the intensity of the information signal more than the threshold value is detected.
  • the convergence of the diffracted light L5 on the conventional optical disk 25 is continued while performing the focus control and the tracking control corresponding to the conventional optical disk 25 in a step 226. Therefore, pieces of information are recorded or reproduced on or from the conventional optical disk 25.
  • the thickness of the optical disk set in the optical disk apparatus 181 can be judged even though the optical disk 171 or 174 is not utilized. Also. pieces of information can be stably recorded or reproduced on or from an optical disk regardless of whether the optical disk is the high density optical disk 182 or the conventional optical disk 25.

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  • Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • General Physics & Mathematics (AREA)
  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Multimedia (AREA)
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Claims (63)

  1. Optisches Bilderzeugungssystem mit:
    einer Lichtquelle (52) zum Aussenden eines Einfallslichtstrahls einer bestimmten Wellenlänge;
    einem Hologramm (26, 26M, 32, 33, 42), das angeordnet ist, um den von der Lichtquelle ausgesandten Einfallslichtstrahl zu empfangen, wobei das Hologramm einen Teil des Einfallslichts ohne jegliche Beugung durchläßt, um einen Strahl eines durchgelassenen Lichts zu bilden, und den restlichen Teil des Einfallslichts beugt, um einen oder mehrere Strahlen eines gebeugten Lichts mit verschiedenen Beugungsordnungen zu bilden, wobei das Hologramm als eine Linse für die Strahlen des gebeugten Lichts dient; und
    Linsenmittel (27) zum Konvergieren des durch das Hologramm gebildeten durchgelassenen Lichts, um einen ersten Brennpunkt (S1) für das durchgelassene Licht zu bilden, und Konvergieren der Strahlen des gebeugten Lichts, die vom Hologramm gebildet wurden, um einen oder mehrere zweite Brennpunkte (S2) für die Strahlen des gebeugten Lichts zu bilden, wobei der erste Brennpunkt und die zweiten Brennpunkte auf einer Seite des Linsenmittels liegen; dadurch gekennzeichnet, daß:
       Licht der bestimmten Wellenlänge durch das Linsenmittel (27) zu sowohl dem ersten Brennpunkt (51) als auch dem oder jedem zweiten Brennpunkt (52) konvergiert wird.
  2. Optisches Bilderzeugungssystem nach Anspruch 1, in welchem ein Beugungsgittermuster (26A) im Hologramm (26) in einer konzentrischen Kreisform ausgebildet ist.
  3. Optisches Bilderzeugungssystem nach Anspruch 1 oder 2, in welchem das Hologramm eine Beugungsvorrichtung vom Phasenmodulationstyp ist.
  4. Optisches Bilderzeugungssystem nach Anspruch 3, in welchem ein Phasenmodulationsgrad von durch das Hologramm durchgehendem Licht geringer als 2π Radiant ist.
  5. Optisches Bilderzeugungssystem nach Anspruch 3 oder 4, in welchem das Hologramm (26) eine Beugungsvorrichtung vom Relieftyp ist.
  6. Optisches Bilderzeugungssystem nach Anspruch 5, wenn abhängig von Anspruch 4, in welchem eine Höhe H eines im Hologramm (26) ausgebildeten Reliefs eingestellt ist auf: H < λ / (n(λ) - 1), worin λ die bestimmte Wellenlänge des Einfallslichts bezeichnet und n(λ) den Brechungsindex des Materials des Hologramms (26) für das Einfallslicht mit der Wellenlänge λ bezeichnet.
  7. Optisches Bilderzeugungssystem nach Anspruch 5 oder 6, in welchem ein Beugungsgittermuster (26A) des Hologramms (26) in einer stufenartigen Querschnittform ausgebildet ist.
  8. Optisches Bilderzeugungssystem nach Anspruch 7, in welchem des Beugungsgittermuster (26A) des Hologramms (26) in einer konzentrischen Kreisform ausgebildet und in mehrere Blöcke konzentrisch unterteilt ist;
       jeder Block eine Treppe aufweist; und der Neigungswinkel der Treppe sich in Richtung auf den Umfang des Beugungsgittermusters des Hologramms allmählich reduziert, um die Beugungseffizienz des Hologramm in Richtung auf den Umfang des Musterbereichs allmählich zu reduzieren.
  9. Optisches Bilderzeugungssystem nach Anspruch 7, in welchem das Beugungsgittermuster (26A) des Hologramms (26) in einer konzentrischen Kreisform ausgebildet und in mehrere, in einem zentralen Teil des Beugungsgittermusters plazierte erste Blöcke und mehrere, in einem Umfangsteil des Beugungsgittermusters plazierte zweite Blöcke konzentrisch unterteilt ist;
    jeder erste Block eine erste Treppe aufweist,
    jeder zweite Block eine zweite Treppe aufweist, wobei die Zahl von Treppenstufen in der zweiten Treppe geringer als die in der ersten Treppe ist, die ersten und zweiten Neigungswinkel der ersten und zweiten Treppen sich in Richtung auf den Umfang des Beugungsgittermusters des Hologramms jeweils allmählich reduzieren, um die Beugungseffizienz des Hologramms in Richtung auf den Umfang des Musterbereichs allmählich zu reduzieren;
    und der zweite Neigungswinkel geringer als der erste Neigungswinkel ist.
  10. Optisches Bilderzeugungssystem nach Anspruch 7, in welchem das Beugungsgittermuster des Hologramms in einer konzentrischen Kreisform ausgebildet und in mehrere Blöcke konzentrisch unterteilt ist;
       jeder Block eine Treppe aufweist und der Neigungswinkel der Treppe sich einwärts des Beugungsgittermusters des Hologramms allmählich reduziert, um die Beugungseffizienz des Hologramms einwärts des Musterbereichs allmählich zu reduzieren.
  11. Optisches Bilderzeugungssystem nach Anspruch 7, in welchem das Beugungsgittermuster des Hologramms in einer konzentrischen Kreisform ausgebildet und in mehrere, in einem zentralen Teil des Beugungsgittermusters plazierte erste Blöcke und mehrere, in einem Umfangsteil des Beugungsgittermusters plazierte zweite Blöcke konzentrisch unterteilt ist,
    jeder erste Block eine erste Treppe aufweist,
    jeder zweite Block eine zweite Treppe aufweist, wobei die Zahl von Treppenstufen in der zweiten Treppe höher als die in der ersten Treppe ist,
    erste und zweite Neigungswinkel der ersten und zweiten Treppen einwärts des Beugungsgittermusters des Hologramms sich jeweils allmählich reduzieren, um die Beugungseffizienz des Hologramms einwärts des Musterbereichs allmählich zu reduzieren, und
    der zweite Neigungswinkel höher als der erste Neigungswinkel ist.
  12. Optisches Bilderzeugungssystem nach Anspruch 1, in welchem das Hologramm eine Beugungsvorrichtung vom Phasenmodulationstyp ist, die aus einer Flüssigkristallzelle hergestellt ist.
  13. Optisches Bilderzeugungssystem nach Anspruch 1, in welchem das Hologramm eine Beugungsvorrichtung vom Phasenmodulationstyp ist, die auf einem aus einem Material mit Doppelbrechung hergestellten Substrat plaziert ist.
  14. Optisches Bilderzeugungssystem nach einem der vorhergehenden Ansprüche, in welchem die Positionsbeziehung zwischen dem Linsenmittel und dem Hologramm festgelegt ist.
  15. Optisches Bilderzeugungssystem nach Anspruch 14, in welchem das Hologramm auf einer Linsenoberfläche des Linsenmittels (46, 47) gebildet ist.
  16. Optisches Bilderzeugungssystem nach Anspruch 15, in welchem das Hologramm (26, 32 oder 42) auf einer Linsenoberfläche des Linsenmittels (46) plaziert ist, die eine höhere Krümmung als andere Linsenoberflächen des Linsenmittels aufweist.
  17. Optisches Bilderzeugungssystem nach Anspruch 15, in welchem das Hologramm auf einer Linsenoberfläche des Linsenmittels (47) plaziert ist, die eine geringere Krümmung als andere Linsenoberflächen des Linsenmittels aufweist.
  18. Optisches Bilderzeugungssystem nach einem der vorhergehenden Ansprüche, in welchem eine numerische Apertur des Linsenmittels sich bezüglich des durchgelassenen Lichts ändert.
  19. Optisches Bilderzeugungssystem nach Anspruch 18, in welchem ein Beugungsgittermuster in einem ersten Teil einer Lichtdurchgangsfläche des Hologramms entsprechend einer Apertur des Linsenmittels gebildet ist und in einem zweiten Teil der Lichtdurchgangsfläche des Hologramms kein Beugungsgittermuster ausgebildet ist.
  20. Optisches Bilderzeugungssystem nach Anspruch 19, in welchem eine Phase des durch den zweiten Teil der Lichtdurchgangsfläche des Hologramms gehenden Einfallslichts im wesentlichen gleich dem Durchschnittswert von Phasen des durch den ersten Teil der Lichtdurchgangsfläche des Hologramms gehenden Einfallslichts ist.
  21. Optisches Bilderzeugungssystem nach Anspruch 19, in welchem das Beugungsgittermuster in einer stufenartigen Form mit mehreren Treppenstufen ausgebildet ist; und
       eine Oberflächenhöhe des zweiten Teils der Lichtdurchgangsfläche des Hologramms in einer optischen Richtung die gleiche wie eine Höhe einer der von der obersten und untersten Treppenstufe verschiedenen Stufen ist.
  22. Optisches Bilderzeugungssystem nach Anspruch 1, in welchem die Beugungseffizienz des Hologramms bezüglich einer Stelle innerhalb der Lichtdurchgangsfläche variiert.
  23. Optisches Bilderzeugungssystem nach Anspruch 22, in welchem ein Beugungsgittermuster des Hologramms (26, 32, 42) konzentrisch ausgebildet ist, das Hologramm eine Beugungsvorrichtung vom Phasenmodulationstyp ist und ein Phasenmodulationsgrad in einem äußeren Teil des Beugungsgittermusters des Hologramms geringer als der in einem inneren Teil des Beugungsgittermusters des Hologramms ist.
  24. Optisches Bilderzeugungssystem nach Anspruch 23, in welchem ein Beugungsgittermuster des Hologramms (26, 32, 42) konzentrisch ausgebildet ist, das Hologramm eine Beugungsvorrichtung vom Phasenmodulationstyp ist und ein Phasenmodulationsgrad in einem inneren Teil des Beugungsgittermusters des Hologramms geringer als der in einem äußeren Teil des Beugungsgittermusters des Hologramms ist.
  25. Optisches Bilderzeugungssystem nach Anspruch 1, in welchem die ersten und zweiten Brennpunkte, die durch das Hologramm erzeugt werden, an Brennpunktstellen liegen, die sich in der Richtung der optischen Achse des Hologramms und des Linsenmittels voneinander unterscheiden.
  26. Optisches Bilderzeugungssystem nach Anspruch 1, in welchem das durch das Linsenmittel (27) konvergierte durchgelassene Licht durch ein Substrat geht, der erste Brennpunkt des durchgelassenen Lichts an einer um eine erste Dicke von der Oberfläche des Substrats beabstandeten Stelle liegt, ein Strahl des durch das Linsenmittel konvergierten gebeugten Lichts durch das Substrat geht und der zweite Brennpunkt des Strahls des gebeugten Lichts an einer anderen Stelle liegt, die von der Oberfläche des Substrats um eine von der ersten Dicke verschiedenen zweiten Dicke beabstandet ist.
  27. Optisches Bilderzeugungssystem nach Anspruch 1, in welchem das durch das Linsenmittel konvergierte durchgelassene Licht durch ein erstes Substrat (22) geht, der erste Brennpunkt des durchgelassenen Lichts auf einer Informationsaufzeichnungsebene (23) liegt, die von der Oberfläche des ersten Substrats um eine erste Dicke T1 beabstandet ist, ein Strahl eines durch das Linsenmittel konvergierten gebeugten Lichts durch ein zweites Substrat (24) geht und der zweite Brennpunkt des Strahls des gebeugten Lichts bei einer anderen Informationsaufzeichnungsebene (25) liegt, die von der Oberfläche des zweiten Substrats um eine zweite Dicke T2 (T1 < T2) beabstandet ist.
  28. Optisches Bilderzeugungssystem nach Anspruch 1, in welchem ein Strahl eines durch das Linsenmittel konvergierten gebeugten Lichts durch ein erstes Substrat (22) geht, der zweite Brennpunkt des Strahls eines gebeugten Lichts auf einer Informationsaufzeichnungsebene (23) liegt, die von der Oberfläche des ersten Substrats um eine erste Dicke T1 beabstandet ist, das durch das Linsenmittel konvergierte durchgelassene Licht durch ein zweites Substrat (24) geht und der erste Brennpunkt des durchgelassenen Lichts bei einer anderen Informationsaufzeichnungsebene (25) liegt, die von der Oberfläche um eine zweite Dicke T2 (T1 < T2) beabstandet ist.
  29. Optisches Bilderzeugungssystem nach einem der vorhergehenden Ansprüche, worin die ersten und zweiten Brennpunkte an der gegenüberliegenden Seite des Linsenmittels von der Lichtquelle liegen.
  30. Optisches Bilderzeugungssystem nach Anspruch 16, in welchem das Hologramm auf einer Linsenoberfläche an einer Stelle plaziert ist, die näher als diejenigen der anderen Linsenoberflächen des Linsenmittels liegt.
  31. Optisches Bilderzeugungssystem nach Anspruch 17, in welchem das Hologramm auf einer Linsenoberfläche an einer gegenüberliegenden Stelle des Linsenmittels von der Lichtquelle plaziert ist.
  32. Optisches Bilderzeugungssystem nach Anspruch 29, in welchem ein Fernfeldmuster eines von der Lichtquelle ausgesandten Einfallslichts verteilt wird, um eine Intensität des Einfallslichts in Richtung auf einen Umfangsteil des Strahls zu verringern, eine Intensität des durch einen zentralen Teil des Linsenmittels gehenden Einfallslichts mindestens die zweifache derjenigen des Einfallslichts ist, das durch einen Umfangsteil des Linsenmittels geht.
  33. Optikkopfvorrichtung mit:
    einem optischen Bilderzeugungssystem nach einem der Ansprüche 29 bis 32, worin das durchgelassene Licht auf einem ersten Aufzeichnungsmedium konvergiert wird und das gebeugte Licht auf einem oder mehreren zweiten Aufzeichnungsmedien konvergiert wird; und
    einem Photodetektor (57, 63, 36, 104, 138, 143, 153) zum Empfangen des durchgelassenen und gebeugten Lichts, das durch das Linsenmittel auf den ersten und zweiten Aufzeichnungsmedien konvergiert wurde, und Abgeben eines elektronischen Signals gemäß Intensitäten des empfangenen Lichts.
  34. Optikkopfvorrichtung nach Anspruch 33, wenn abhängig von Anspruch 2, in welcher das Beugungsgittermuster in einem ersten Teil einer Lichtdurchgangsfläche des Hologramms entsprechend einer Apertur des Linsenmittels ausgebildet ist und ein anderes Beugungsgittermuster in einem zweiten Teil der Lichtdurchgangsfläche des Hologramms nicht konzentrisch ausgebildet ist, um das Einfallslicht zu beugen.
  35. Optikkopfvorrichtung nach Anspruch 33 oder 34, in welchem das Hologramm (26, 26M, 32, 33, 42) auf einer Ebene angeordnet ist und eine optische Achse des Linsenmittels (27) nicht parallel zu einem Einfallslot der Ebene ist.
  36. Optikkopfvorrichtung nach Anspruch 33, 34 oder 35, in welcher der Photodetektor (57, 63, 64, 104, 138, 143, 153) nahe der Lichtquelle (52) angeordnet ist.
  37. Optikkopfvorrichtung nach einem Ansprüche 33 bis 36, in welcher das von der Lichtquelle ausgesandte Einfallslicht linear polarisiert ist und die Optikkopfvorrichtung ferner aufweist:
    einen Polarisationsstrahlteiler (54, 68), um einen Strahl eines in einer ersten Richtung linear polarisierten Lichts total durchzulassen und einen Strahl eines in einer zur ersten Richtung senkrechten zweiten Richtung linear polarisierten Lichts totalzureflektieren; und
    eine 1/4-λ-Platte (6a) zum Ändern des Einfallslichts, das durch den Polarisationsstrahlteiler durchgeht oder von diesem reflektiert wird, in einen Strahl eines in einer ersten Drehrichtung zirkular polarisierten Lichts, worin ein Strahl eines durchgelassenen Lichts und ein oder mehrere Strahlen eines gebeugten Lichts, das in der ersten Drehrichtung zirkular polarisiert ist, durch die zusammengesetzte Objektivlinse gebildet und auf den Informationsmedien konvergiert werden, um einen Strahl eines durchgelassenen Lichts und einen oder mehrere Strahlen eines gebeugten Lichts zu bilden, das in einer zur ersten Drehrichtung entgegengesetzten zweiten Drehrichtung zirkular polarisiert ist, die Strahlen eines durchgelassenen und gebeugten Lichts, das in der zweiten Drehrichtung zirkular polarisiert ist, in mehrere Strahlen eines Lichts, das in einer zur ersten Richtung senkrechten dritten Richtung linear polarisiert ist, durch die 1/4-λ-Platte geändert werden und die Strahlen eines in der dritten Richtung linear polarisierten Lichts durch den Polarisationsstrahlteiler total-reflektiert oder durch diesen durchgelassen werden, um auf den Photodetektor zu fallen.
  38. Optikkopfvorrichtung nach einem der Ansprüche 33 bis 37, in der der Photodetektor umfaßt:
    einen Servosignaldetektor (SE1 bis SE6) zum Nachweisen eines Servosignals, das in einem der Strahlen eines durchgelassenen und gebeugten Lichts enthalten ist, das in den Aufzeichnungsmedien konvergiert wurde; und
    einen anderen Signaldetektor (60a-d), der an einem Umfang des Servosignaldetektors angeordnet ist, um ein anderes Signal nachzuweisen, das in einem anderen Strahl des durchgelassenen und gebeugten Lichts enthalten ist, das auf den Aufzeichnungsmedien konvergiert wurde.
  39. Optikkopfvorrichtung nach einem der Ansprüche 33 bis 38, in der der Photodetektor aufweist:
       einen Signaldetektor (59) zum Nachweisen eines Brennpunkt-Fehlersignals und eines Nachführungs-Fehlersignals, die in Strahlen eines durchgelassenen und gebeugten Lichts enthalten sind, das auf den Aufzeichnungsmedien konvergiert wurde.
  40. Optikkopfvorrichtung nach einem der Ansprüche 33 bis 39, ferner aufweisend:
       ein Neuformungsmittel (72) zum Neuformen des von der Lichtquelle ausgesandten Einfallslichts, wobei die Strahlen eines durchgelassenen und gebeugten Lichts aus dem neugeformten Licht gebildet werden.
  41. Optikkopfvorrichtung nach einem der Ansprüche 33 bis 40, worin das Linsenmittel (27) dafür angepaßt ist, das durch das Hologramm gebildete durchgelassene Licht auf einem Ausgangsweg zu konvergieren, um es durch eine Rückseite eines ersten Informationsmediums durchzulassen und einen ersten Brennpunkt für das durchgelassene Licht an einer Vorderseite des ersten Informationsmediums zu bilden, und den oder jeden Strahl eines gebeugten Lichts, das durch das Hologramm gebildet wurde, auf dem Ausgangsweg zu konvergieren, um ihn oder sie durch Rückseiten eines oder mehrerer zweiter Informationsmedien durchzulassen und einen oder mehrere zweite Brennpunkte für die Strahlen eines gebeugten Lichts an Vorderseiten des oder jedes zweiten Informationsmediums in einer 1-zu-1-Entsprechung zu bilden, wobei das durchgelassene Licht an der Vorderseite des ersten Informationsmediums reflektiert wird und wieder durch das Linsenmittel und das Hologramm auf einem Eingangsweg geht und der oder jeder Strahl eines gebeugten Lichts an den Vorderseiten des oder jedes zweiten Informationsmediums reflektiert wird und wieder durch das Linsenmittel und das Hologramm auf dem Eingangsweg geht, und worin der Photodetektor aufweist:
       einen Photodetektor (57, 63, 64, 104, 138, 143, 153) zum Nachweisen des Strahls eines durchgelassenen Lichts oder eines Strahls eines gebeugten Lichts, das durch das Linsenmittel und das Hologramm auf dem Eingangsweg geht, und Erzeugen eines Informationssignals und von Servosignalen, die ein Brennpunkt-Fehlersignal und ein Nachführungs-Fehlersignal darstellen, aus dem Strahl eines durchgelassenen Lichts oder dem Strahl eines gebeugten Lichts, wobei das Informationssignal eine auf dem ersten Informationsmedium oder einem zweiten Informationsmedium entsprechend dem Strahl eines gebeugten Lichts aufgezeichnete Information ausdrückt, das Brennpunkt-Fehlersignal einen Brennpunktfehler des Strahls eines durchgelassenen Lichts, der auf dem ersten Informationsmedium konvergiert wurde, oder einen Brennpunktfehler des Strahls eines gebeugten Lichts angibt, der auf dem zweiten Informationsmedium konvergiert wurde, und das Nachführungs-Fehlersignal einen Nachführungsfehler des Strahls eines durchgelassenen Lichts, der auf dem ersten Informationsmedium konvergiert wurde, oder einen Nachführungsfehler des Strahls eines gebeugten Lichts angibt, der auf dem zweiten Informationsmediums konvergiert wurde.
  42. Optikkopfvorrichtung nach Anspruch 41, ferner aufweisend:
    ein Wellenfrontänderungsmittel (56, 62, 66) zum Ändern einer Wellenfront des durchgelassenen Lichts oder des Strahls eines gebeugten Lichts, das durch das Linsenmittel und das Hologramm auf dem Eingangsweg durchgeht, um einen Strahl eines ersten Informationslichts und einen Strahl eines zweiten Informationslichts zu bilden, wobei das erste Informationslicht einen dritten Brennpunkt vor dem Photodetektor hat und das zweite Informationslicht einen vierten Brennpunkt hinter dem Photodetektor hat, und worin
    der Photodetektor ein Paar Brennpunktfehlerdetektoren (59) zum Nachweisen einer Intensität des ersten Informationslichts und einer Intensität des zweiten Informationslichts aufweist, die durch das Wellenfrontänderungsmittel gebildet wurden, um das Brennpunkt-Fehlersignal zu erzeugen, wobei eine Position des Linsenmittels gemäß dem Brennpunkt-Fehlersignal eingestellt wird, um das durchgelassene Licht oder den Strahl eines gebeugten Lichts auf dem ersten Informationsmedium oder dem zweiten Informationsmedium zu fokussieren.
  43. Optikkopfvorrichtung nach Anspruch 41, ferner aufweisend:
       ein zweites Hologramm (56, 62, 66) mit mehreren Beugungsgittermustern zum Empfangen des durchgelassenen Lichts oder des Strahls eines gebeugten Lichts, das durch das Linsenmittel und das Hologramm auf dem Eingangsweg durchgeht, und Ändern einer Wellenfront des durchgelassenen Lichts oder des Strahls eines gebeugten Lichts, das durch jedes Beugungsgittermuster durchgeht, um einen Strahl eines Informationslichts für jedes Beugungsgittermuster zu bilden, wobei die Strahlen eines Informationslichts durch den Photodetektor nachgewiesen werden, um das Informationssignal zu erzeugen.
  44. Optikkopfvorrichtung nach Anspruch 41, ferner aufweisend:
       eine eine astigmatische Aberration erzeugende Einheit (62, 66), um eine astigmatische Aberration in dem durchgelassenen Licht oder dem Strahl eines gebeugten Lichts zu erzeugen, das durch das Linsenmittel und das Hologramm auf dem Eingangsweg durchgeht, um eine Wellenfront des durchgelassenen Lichts oder des Strahls eines gebeugten Lichts zu ändern und mehrere Informationslichtstrahlen zu bilden, und wobei der Photodetektor aufweist:
       einen Quadranten-Photodetektor (63) mit vier Nachweissektionen zum Nachweisen von Intensitäten der Informationslichtstrahlen, die durch die eine astigmatische Aberration erzeugende Einheit gebildet wurden, um das Informationssignal und die Servosignale zu erzeugen, die das Brennpunkt-Fehlersignal und das Nachführungs-Fehlersignal darstellen, wobei die Position des Linsenmittels gemäß dem Brennpunkt-Fehlersignal eingestellt wird, um das durchgelassene Licht oder den Strahl eines gebeugten Lichts auf dem ersten Informationsmedium oder dem zweiten Informationsmedium zu fokussieren.
  45. Optikkopfvorrichtung nach Anspruch 44, in der die eine astigmatische Aberration erzeugende Einheit (42, 66) aus einer ebenen parallelen Platte gebildet ist, von der ein Einfallslot gegen eine optische Achse geneigt ist.
  46. Optikkopfvorrichtung nach Anspruch 44, in der die eine astigmatische Aberration erzeugende Einheit aus einer zylindrischen Linse geschaffen ist.
  47. Optikkopfvorrichtung nach einem der Ansprüche 41 bis 46, in der ein Beugungsgittermuster auf einer flachen Oberfläche des Hologramms gezeichnet ist, und
       ein Einfallslot der flachen Oberfläche des Hologramms gegen eine optische Achse des Linsenmittels geneigt ist.
  48. Optikkopfvorrichtung nach Anspruch 41, in der die erste Dicke des ersten Informationsmediums geringer als die zweite Dicke des zweiten Informationsmediums ist, und die Optikkopfvorrichtung ferner aufweist:
    einen Strahlteiler (82) zum Durchlassen eines Strahls eines gebeugten Lichts, das durch das Hologramm auf dem Eingangsweg ohne jegliche Beugung durchgelassen wurde, um einen Strahl eines ersten Informationslichts mit einer astigmatischen Aberration zu bilden, und Reflektieren des durchgelassenen Lichts, das durch das Hologramm auf dem Eingangsweg ohne jegliche Beugung durchgelassen wurde; und
    eine Wellenfrontänderungseinheit (56) zum Ändern einer Wellenfront des durchgelassenen Lichts, das durch den Strahlteiler reflektiert wurde, um mehrere Strahlen eines zweiten Informationslichts zu bilden, und der Photodetektor aufweist:
    einen Quadranten-Photoetektor (63) mit vier Nachweissektionen zum Nachweisen einer Intensität des ersten Informationslichts, das durch den Strahlteiler durchgelassen wurde, um ein erstes Informationssignal und erste Servosignale zu erzeugen, die ein erstes Brennpunkt-Fehlersignal und ein erstes Nachführungs-Fehlersignal darstellen;
    ein Paar Brennpunktfehlerdetektoren (59) zum Nachweisen von Intensitäten von zwei Strahlen eines zweiten Informationslichts, die durch Wellenfrontänderungsmittel gebildet wurde, um ein zweites Informationssignal und ein zweites Brennpunkt-Fehlersignal zu erzeugen; und
    mehrere Nachführungsfehlerdetektoren (60a, 60b, 60c, 60d) zum Nachweisen von Intensitäten der Strahlen eines zweiten Informationslichts, die durch das Wellenfrontänderungsmittel gebildet wurden, um ein zweites Nachführungs-Fehlersignal zu erzeugen, wobei eine Positionsbeziehung zwischen dem Linsenmittel und dem zweiten Informationsmedium gemäß den ersten Servosignalen eingestellt wird, um das gebeugte Licht auf dem zweiten Informationsmedium zu fokussieren, eine Positionsbeziehung zwischen dem Linsenmittel und dem ersten Informationsmedium gemäß dem zweiten Brennpunkt-Fehlersignal und dem zweiten Nachführungs-Fehlersignal eingestellt wird, um das durchgelassene Licht auf dem ersten Informationsmedium zu fokussieren, das erste Informationssignal die auf dem zweiten Informationsmedium aufgezeichnete Information ausdrückt und das zweite Informationssignal die auf dem ersten Informationsmedium aufgezeichnete Information ausdrückt.
  49. Optikkopfvorrichtung nach Anspruch 41, worin die erste Dicke des ersten Informationsmediums geringer als die zweite Dicke des zweiten Informationsmediums ist, wobei die Optikkopfvorrichtung ferner aufweist:
    einen Strahlteiler (92) mit einer Wellenfrontänderungseinheit (93) zum Durchlassen des Strahls eines durchgelassenen Lichts, das durch das Hologramm ohne jegliche Beugung auf dem Eingangsweg durchgelassen wurde, um einen Strahl eines ersten Informationslichts mit einer astigmatischen Aberration zu bilden, und Beugen und Reflektieren des gebeugten Lichts, welches durch das Hologramm ohne jegliche Beugung auf dem Eingangsweg durchgelassen wird und auf die Wellenfrontänderungseinheit fällt, um mehrere Strahlen eines zweiten Informationslichts zu bilden, und
    der Photodetektor aufweist:
    einen Quadranten-Photodetektor (63) mit vier Nachweissektionen zum Nachweisen einer Intensität des ersten Informationslichts, das durch den Strahlteiler durchgelassen wurde, um ein erstes Informationssignal und erste Servosignale zu erzeugen, die ein erstes Brennpunkt-Fehlersignal und ein erstes Nachführungs-Fehlersignal darstellen;
    ein Paar Brennpunktfehlerdetektoren (59) zum Nachweisen von Intensitäten von zwei Strahlen eines zweiten Informationslichts, die durch die Wellenfrontänderungseinheit des Strahlteilers gebildet wurden, um ein zweites Informationssignal und ein zweites Brennpunkt-Fehlersignal zu erzeugen; und
    mehrere Nachführungsfehlerdetektoren (60a, 60b, 60c, 60d) zum Nachweisen von Intensitäten der Strahlen eines zweiten Informationslichts, die durch die Wellenfrontänderungseinheit des Strahlteilers gebildet wurden, um ein zweites Nachführungs-Fehlersignal zu erzeugen, wobei eine Positionsbeziehung zwischen dem Linsenmittel und dem ersten Informationsmedium gemäß den ersten Servosignalen eingestellt wird, um das durchgelassene Licht auf dem ersten Informationsmedium zu fokussieren, eine Positionsbeziehung zwischen dem Linsenmittel und dem zweiten Informationsmedium gemäß dem zweiten Brennpunkt-Fehlersignal und dem zweiten Nachführungs-Fehlersignal eingestellt wird, um das gebeugte Licht auf dem zweiten Informationsmedium zu fokussieren, das erste Informationssignal die auf dem ersten Informationsmedium aufgezeichnete Information ausdrückt und das zweite Informationssignal die auf dem zweiten Informationsmedium aufgezeichnete Information ausdrückt.
  50. Optikkopfvorrichtung nach Anspruch 41, in der die erste Dicke des ersten Informationsmediums geringer als die zweite Dicke des zweiten Informationsmediums ist, das durchgelassene Licht im Defokus (in defocus) an der Vorderseite des zweiten Informationsmediums durch das Linsenmittel auf dem Ausgangsweg konvergiert und reflektiert wird, um ohne jegliche Beugung auf dem Eingangsweg wieder durch das Linsenmittel und das Hologramm zu gehen, und die Optikkopfvorrichtung ferner aufweist:
    einen Strahlteiler (102) mit einer Wellenfrontänderungseinheit (103) zum Durchlassen des Strahls eines gebeugten Lichts, das durch das Hologramm ohne jegliche Beugung auf dem Eingangsweg durchgelassen wurde, um einen Strahl eines ersten Informationslichts mit einer astigmatischen Aberration zu bilden, und Beugen des durchgelassenen Lichts, welches auf dem zweiten Informationsmedium im Defokus konvergiert wird und auf die Wellenfrontänderungseinheit fällt, um mehrere Strahlen eines zweiten Informationslichts zu bilden, und der Photodetektor (104) aufweist
    einen ersten Photodetektor (104) zum Nachweisen, im Defokus, einer Intensität des ersten Informationslichts, das durch den Strahlteiler durchgelassen wurde, um ein erstes Informationssignal zu erzeugen, das die auf dem zweiten Informationsmedium aufgezeichnete Information ausdrückt; und
    einen zweiten Photodetektor (59) zum Nachweisen von Intensitäten der Strahlen eines zweiten Informationslichts, das durch die Wellenfrontänderungseinheit des Strahlteilers gebeugt wurde, um ein Brennpunkt-Fehlersignal zu erzeugen, wobei eine Positionsbeziehung zwischen dem Linsenmittel und dem zweiten Informationsmedium gemäß dem Brennpunkt-Fehlersignal eingestellt wird, um das gebeugte Licht auf dem zweiten Informationsmedium zu fokussieren.
  51. Optikkopfvorrichtung nach Anspruch 41, in der die erste Dicke des ersten Informationsmediums größer als die zweite Dicke des zweiten Informationsmediums ist, wobei die Optikkopfvorrichtung ferner aufweist:
    einen Strahlteiler (82) zum Durchlassen des Strahls eines gebeugten Lichts, das durch das Hologramm auf dem Eingangsweg wieder gebeugt wurde, um einen Strahl eines ersten Informationslichts mit einer astigmatischen Aberration zu bilden, und Reflektieren des durch das Hologramm auf dem Eingangsweg gebeugten durchgelassenen Lichts; und
    eine Wellenfrontänderungseinheit (56) zum Ändern einer Wellenfront des durch den Strahlteiler reflektierten durchgelassenen Lichts, um mehrere Strahlen eines zweiten Informationslichts zu bilden, und der Photodetektor aufweist
    einen Quadranten-Photodetektor (63) mit vier Nachweissektionen zum Nachweisen einer Intensität des durch den Strahlteiler durchgelassenen ersten Informationslichts, um ein erstes Informationssignal und erste Servosignale zu erzeugen, die ein erstes Brennpunkt-Fehlersignal und ein erstes Nachführungs-Fehlersignal darstellen;
    ein Paar Brennpunktfehlerdetektoren (59) zum Nachweisen von Intensitäten von zwei Strahlen eines zweiten Informationslichts, die durch das Wellenfrontänderungsmittel gebildet wurden, um ein zweites Informationssignal und ein zweites Brennpunkt-Fehlersignal zu erzeugen; und
    mehrere Nachführungsfehlerdetektoren (60a, 60b, 60c, 60d) zum Nachweisen von Intensitäten der Strahlen eines zweiten Informationslichts, die durch die Wellenfrontänderungseinheit gebildet wurden, um ein zweites Nachführungs-Fehlersignal zu erzeugen, wobei eine Positionsbeziehung zwischen dem Linsenmittel und dem zweiten Informationsmedium gemäß den ersten Servosignalen eingestellt wird, um das gebeugte Licht auf dem zweiten Informationsmedium zu fokussieren, eine Positionsbeziehung zwischen dem Linsenmittel und dem ersten Informationsmedium gemäß dem zweiten Brennpunkt-Fehlersignal und dem zweiten Nachführungs-Fehlersignal eingestellt wird, um das durchgelassene Licht auf dem ersten Informationsmedium zu fokussieren, das erste Informationssignal die auf dem zweiten Informationsmedium aufgezeichnete Information ausdrückt und das zweite Informationssignal die auf dem ersten Informationsmedium aufgezeichnete Information ausdrückt.
  52. Optikkopfvorrichtung nach Anspruch 41, in der die erste Dicke des ersten Informationsmediums größer als die zweite Dicke des zweiten Informationsmediums ist, und die Optikkopfvorrichtung ferner aufweist:
       einen Strahlteiler (92) mit einer Wellenfrontänderungseinheit (93) zum Durchlassen des durch das Hologramm auf dem Eingangsweg gebeugten durchgelassenen Lichts, um einen Strahl eines ersten Informationslichts mit einer astigmatischen Aberration zu bilden, und Beugen und Reflektieren des gebeugten Lichts, welches durch das Hologramm auf dem Eingangsweg wieder gebeugt wird und auf die Wellenfrontänderungseinheit fällt, um mehrere Strahlen eines zweiten Informationslichts zu bilden, und
    der Photodetektor aufweist
    einen Quadranten-Photodetektor (63) mit vier Nachweissektionen zum Nachweisen einer Intensität des durch den Strahlteiler durchgelassenen ersten Informationslichts, um ein erstes Informationssignal und erste Servosignale zu erzeugen, die ein erstes Brennpunkt-Fehlersignal und ein erstes Nachführungs-Fehlersignal darstellen;
    ein Paar Brennpunktfehlerdetektoren (59) zum Nachweisen von Intensitäten von zwei Strahlen eines zweiten Informationslichts, die durch die Wellenfrontänderungseinheit des Strahlteilers gebildet wurden, um ein zweites Informationssignal und ein zweites Brennpunkt-Fehlersignal zu erzeugen; und
    mehrere Nachführungsfehlerdetektoren (60a, 60b, 60c, 60d) zum Nachweisen von Intensitäten von vier Strahlen eines zweiten Informationslichts, die durch die Wellenfrontänderungseinheit des Strahlteilers gebildet wurden, um ein zweites Nachführungs-Fehlersignal zu erzeugen, wobei eine Positionsbeziehung zwischen dem Linsenmittel und dem ersten Informationsmedium gemäß den ersten Servosignalen eingestellt wird, um das durchgelassene Licht auf dem ersten Informationsmedium zu fokussieren, eine Positionsbeziehung zwischen dem Linsenmittel und dem zweiten Informationsmedium gemäß dem zweiten Brennpunkt-Fehlersignal und dem zweiten Nachführungs-Fehlersignal eingestellt wird, um das gebeugte Licht auf dem zweiten Informationsmedium zu fokussieren, das erste Informationssignal die auf dem ersten Informationsmedium aufgezeichnete Information ausdrückt und das zweite Informationssignal die auf dem zweiten Informationsmedium aufgezeichnete Information ausdrückt.
  53. Optikkopfvorrichtung nach Anspruch 41, in der das Hologramm (135, 142) in einen zentralen Bereich (135a, 142a) und einen Umfangsbereich (135b, 142b, 142c) unterteilt ist, der den zentralen Bereich umgibt,
    ein erstes Beugungsgittermuster in dem zentralen Bereich des Hologramms in einer konzentrischen Kreisform gezeichnet ist,
    ein zweites Beugungsgittermuster in dem Umfangsbereich des Hologramms in einer nichtkonzentrischen Kreisform gezeichnet ist,
    das durchgelassene Licht, das durch den zentralen Bereich des Hologramms ohne jegliche Beugung auf dem Ausgangsweg durchgelassen wird, durch das Hologramm ohne jegliche Beugung auf dem Eingangsweg durchgelassen wird,
    ein Teil des von der Lichtquelle ausgesandten Einfallslichts durch den Umfangsbereich des Hologramms auf dem Ausgangsweg durchgeht, um einen Strahl eines Umfangslichts zu bilden,
    der Strahl eines Umfangslichts durch das Linsenmittel konvergiert wird, um einen konvergierenden Fleck zu bilden, der den ersten Brennpunkt auf dem ersten Informationsmedium umgibt,
    ein Teil des Umfangslichts, der auf dem ersten Informationsmedium reflektiert wird, durch das Linsenmittel konvergiert und im Umfangsbereich des Hologramms auf dem Eingangsweg gebeugt wird, um einen Strahl eines Rauschen unterdrükkenden Lichts zu bilden, und der Photodetektor aufweist
    einen ersten Photodetektor (64) zum Nachweisen einer Intensität des durchgelassenen Lichts, das durch den zentralen Bereich des Hologramms ohne jegliche Beugung auf dem Eingangsweg durchgelassen wurde, um eine erste Informationskomponente (SC1) zu erzeugen, die eine auf dem ersten Informationsmedium aufgezeichnete Information ausdrückt; und
    einen zweiten Photodetektor (138) zum Nachweisen einer Intensität des Rauschen unterdrückenden Lichts, das im Umfangsbereich des Hologramms auf dem Eingangsweg gebeugt wurde, um eine zweite Informationskomponente (SC2) zu erzeugen, die die Information ausdrückt, wobei ein Informationssignal Snc mit unterdrücktem Rauschen erhalten wird, indem die erste Informationssignalkomponente (SC1) und eine multiplizierte zweite Informationssignalkomponente (R*SC2) addiert werden, welche durch Multiplizieren der zweiten Informationskomponente (SC2) mit einem Gewichtungsfaktor (R) erhalten wird.
  54. Optikkopfvorrichtung nach Anspruch 53, in der
    der Umfangsbereich des Hologramms in einen Umfangsbereich (142b) auf einer ersten Seite und einen Umfangsbereich (142c) auf einer zweiten Seite unterteilt ist, die mit dem zentralen Bereich zwischen dem Umfangsbereich auf der ersten und zweiten Seite einander gegenüberliegen, ein Fernfeldmuster des von Lichtquelle ausgesandten Einfallslichts verteilt wird, um eine Intensität des Einfallslichts in Richtung auf einen Umfangsteil des Einfallslichtstrahls zu verringern,
    ein Querschnittstrahlprofil des von der Lichtquelle ausgesandten Einfallslichts in einer elliptischen Form vorliegt, in der ein strahldivergenter Winkel des Einfallslichts in einer senkrechten Richtung größer ist als der in einer horizontalen Richtung,
    das Einfallslicht, das auf einer Seite seines Strahls in der senkrechten Richtung plaziert ist, durch den Umfangsbereich auf der ersten Seite des Hologramms geht, um eine Intensität des Einfallslichts zu reduzieren,
    das Einfallslicht, das an der anderen Seite seines Strahls in der senkrechten Richtung plaziert ist, durch den Umfangsbereich auf der zweiten Seite des Hologramms geht, um eine Intensität des Einfallslichts zu verringern, und
    ein Querschnittstrahlprofil des durchgelassenen Lichts, das durch das Hologramm auf dem Ausgangsweg geht, in einer kreisförmigen Form vorliegt.
  55. Optikkopfvorrichtung nach Anspruch 53, in der
       der Umfangsbereich des Hologramms in einen Umfangsbereich (142b) auf einer ersten Seite und einen Umfangsbereich (142c) auf einer zweiten Seite unterteilt ist, die mit dem zentralen Bereich zwischen dem Umfangsbereich auf der ersten und zweiten Seite einander gegenüberliegen, und der zweite Photodetektor aufweist:
    einen ersten Rauschunterdrückungsdetektor (138a) zum Nachweisen einer Intensität des Rauschen unterdrückenden Lichts, das durch den Umfangsbereich auf der ersten Seite des Hologramms auf dem Eingangsweg durchgelassen wurde, um eine dritte Informationssignalkomponente (SC3) zu erzeugen, die die Information ausdrückt; und
    einen zweiten Rauschunterdrückungsdetektor (138b) zum Nachweisen einer Intensität des Rauschen unterdrückenden Lichts, das durch den Umfangsbereich auf der zweiten Seite des Hologramms auf dem Eingangsweg durchgelassen wurde, um eine vierte Informationssignalkomponente (SC4) zu erzeugen, die die Information ausdrückt, wobei das Informationssignal (Snc) mit unterdrücktem Rauschen gemäß einer Gleichung: Snc = SC2 + R1* SC3 + R2* SC4
    erhalten wird, worin R1 und R2 Gewichtungsfaktoren sind.
  56. Optikkopfvorrichtung nach Anspruch 41, in der
    eine Positionsbeziehung zwischen der Lichtquelle und dem Photodetektor festgelegt ist, und
    die Lichtquelle nahe dem Photodetektor plaziert ist.
  57. Optikkopfvorrichtung nach Anspruch 41, in der
    das von der Lichtquelle ausgesandte Einfallslicht in einer ersten Richtung linear polarisiert ist,
    das durchgelassene Licht und das gebeugte Licht in einer zur ersten Richtung senkrechten zweiten Richtung auf dem Eingangsweg linear polarisiert sind,
    und die Optikkopfvorrichtung ferner aufweist:
    ein transparentes Substrat (163);
    einen polarisierenden Trennfilm (162), der auf einer Vorderfläche des transparenten Substrats angeordnet ist, um das in der ersten Richtung polarisierte Einfallslicht auf dem Ausgangsweg zu reflektieren und das durchgelassene Licht oder das gebeugte Licht, das in der zweiten Richtung linear polarisiert ist, auf dem Eingangsweg zu brechen; und
    ein zweites Hologramm (164), das auf einer Rückseite des transparenten Substrats angeordnet ist, um das durchgelassene Licht oder das durch den polarisierenden Trennfilm auf dem Eingangsweg gebrochene gebeugte Licht zu beugen, um mehrere Strahlen eines Informationslichts zu bilden, wobei Intensitäten der Strahlen eines Informationslichts durch den Photodetektor nachgewiesen werden, um das Informationssignal zu erzeugen.
  58. Informationsreproduzierverfahren mit den Schritten:
    Aussenden eines Einfallslichtstrahls mit einer bestimmten Wellenlänge von einer Lichtquelle (52),
    Fokussieren des Einfallslichtstrahls auf einem Informationsmedium, und
    Nachweisen einer Information, die auf dem Informationsmedium von dem Einfallslichtstrahl aufgezeichnet wurde, der auf dem Informationsmedium reflektiert wurde,
       dadurch gekennzeichnet, daß
    der Schritt eines Fokussierens des Einfallslichtstrahls die Schritte aufweist:
    Vorbereiten eines ersten Informationsmediums und eines oder mehrerer zweiter Informationsmedien, die innerhalb eines Substrats bei verschiedenen Dicken als das Informationsmedium plaziert wurden;
    Empfangen des von der Lichtquelle ausgesandten Einfallslichtstrahls in einem Hologramm (26, 26M, 32, 33, 42);
    Durchlassen eines Teils des Einfallslichts ohne jegliche Beugung auf einem Ausgangsweg im Hologramm, um einen Strahl eines durchgelassenen Lichts zu bilden;
    Beugen des restlichen Teils des Einfallslichts auf dem Ausgangsweg im Hologramm, um einen oder mehrere Strahlen eines gebeugten Lichts mit verschiedenen Beugungsordnungen zu bilden;
    Konvergieren des durchgelassenen Lichts in einem Linsenmittel (27) auf dem Ausgangsweg, um einen ersten Brennpunkt für das durchgelassene Licht auf dem ersten Informationsmedium zu schaffen, wobei das durchgelassene Licht auf dem ersten Informationsmedium reflektiert wird und wieder durch das Linsenmittel und das Hologramm auf einem Eingangsweg geht;
    Konvergieren der Strahlen eines gebeugten Lichts in dem Linsenmittel auf dem Ausgangsweg, um einen oder mehrere Brennpunkte für die Strahlen eines gebeugten Lichts auf den zweiten Informationsmedien in einer 1-zu-1-Entsprechung zu schaffen, wobei die Strahlen eines gebeugten Lichts auf den zweiten Informationsmedien reflektiert werden und wieder durch das Linsenmittel und das Hologramm auf dem Eingangsweg gehen, und
    der Schritt zum Feststellen einer Information die Schritte aufweist:
    Nachweisen einer Intensität des durchgelassenen Lichts und von Intensitäten der Strahlen eines gebeugten Lichts, das durch das Linsenmittel und das Hologramm auf dem Eingangsweg geht; und
    Reproduzieren einer Information, die auf dem ersten Informationsmedium und den zweiten Informationsmedien aufgezeichnet wurde, aus der Intensität des durchgelassenen Lichts und den Intensitäten der Strahlen des gebeugten Lichts.
  59. Fokussierverfahren nach Anspruch 58, worin:
    der Schritt eines Fokussierens des Einfallslichtstrahls ferner den Schritt aufweist:
    Bewegen der zusammengesetzten Objektivlinse in einer Richtung, um die zusammengesetzte Objektivlinse und das erste Informationsmedium oder ein zweites Informationsmedium zu verringern oder zu vergrößern; und
    der Schritt eines Reproduzierens von Information die Schritte umfaßt:
    Erzeugen eines Informationssignals und von Servosignalen, die ein Brennpunkt-Fehlersignal und ein Nachführungs-Fehlersignal darstellen, aus dem Strahl eines durchgelassenen Lichts oder einem Strahl eines gebeugten Lichts, wobei das Informationssignal eine auf dem ersten Informationsmedium oder einem zweiten Informationsmedium aufgezeichnete Information ausdrückt, entsprechend dem Strahl eines gebeugten Lichts, wobei das Brennpunkt-Fehlersignal einen Brennpunktfehler des Strahls eines durchgelassenen Lichts angibt, das auf dem ersten Informationsmedium konvergiert wurde, oder einen Brennpunktfehler des Strahls eines gebeugten Lichts, das auf dem zweiten Informationsmedium konvergiert wurde, und das Nachführungs-Fehlersignal einen Nachführungsfehler des Strahls eines durchgelassenen Lichts angibt, das auf dem ersten Informationsmedium konvergiert wurde, oder einen Nachführungsfehler des Strahls eines gebeugten Lichts, das auf dem zweiten Informationsmedium konvergiert wurde;
    Beurteilen, ob eine Intensität des Brennpunkt-Fehlersignals größer als ein Schwellenwert ist oder nicht; und
    Einstellen der Position der zusammengesetzten Objektivlinse, um die Intensität des Brennpunkt-Fehlersignals in Fällen, in denen die Intensität des Brennpunkt-Fehlersignals größer als der Schwellenwert ist, auf Null zu verringern.
  60. Informationsreproduzierverfahren nach Anspruch 58, worin:
    der Schritt eines Vorbereitens eines ersten Informationsmediums die Schritte aufweist:
    Vorbereiten einer optischen Platte (171) mit einem ersten Bereich (171a) einer ersten Dicke und einem zweiten Bereich (171b) einer zweiten Dicke, wobei eine Aufzeichnungsinformation mit einer hohen Dichte auf einer ersten Vorderseite der optischen Platte aufgezeichnet wird, die im ersten Bereich plaziert ist, und eine Unterscheidungsinformation, die angibt, daß die Aufzeichnungsinformation auf der ersten Vorderseite der optischen Platte aufgezeichnet ist, mit einer gewöhnlichen Dichte auf einer zweiten Vorderseite der optischen Platte aufgezeichnet wird, die im zweiten Bereich plaziert ist;
    Drehen der optischen Platte mit einer gleichmäßigen Geschwindigkeit;
    Bewegen einer zusammengesetzten Objektivlinse in einer Richtung, um eine Distanz zwischen der zusammengesetzten Objektivlinse und der optischen Platte zu verringern oder zu vergrößern; und
    der Schritt eines Reproduzierens von Information die Schritte umfaßtt:
    Erzeugen eines Aufzeichnungsinformationssignals und erster Servosignale, die ein erstes Brennpunkt-Fehlersignal und ein erstes Nachführungs-Fehlersignal darstellen, aus dem durchgelassenen Licht, wobei das Aufzeichnungsinformationssignal die auf der ersten Vorderseite der optischen Platte aufgezeichnete Aufzeichnungsinformation angibt, das erste Brennpunkt-Fehlersignal einen Brennpunktfehler des auf der ersten Vorderseite der optischen Platte konvergierten durchgelassenen Lichts angibt und das erste Nachführungs-Fehlersignal einen Nachführungsfehler des auf der ersten Vorderseite der optischen Platte konvergierten durchgelassenen Lichts angibt;
    Erzeugen eines Unterscheidungsinformationssignals und zweiter Servosignale, die ein zweites Brennpunkt-Fehlersignal und ein zweites Nachführungs-Fehlersignal darstellen, aus dem gebeugten Licht, wobei das Unterscheidungsinformationssignal die auf der zweiten Vorderseite der optischen Platte aufgezeichnete Unterscheidungsinformation anzeigt, das zweite Brennpunkt-Fehlersignal einen Brennpunktfehler des auf der zweiten Vorderseite der optischen Platte konvergierten gebeugten Lichts angibt und das zweite Nachführungs-Fehlersignal einen Nachführungsfehler des auf der zweiten Vorderseite der optischen Platte konvergierten gebeugten Lichts angibt,
    Konvergieren des gebeugten Lichts auf der zweiten Vorderseite der optischen Platte gemäß den zweiten Servosignalen, um zu beurteilen, ob die Unterscheidungsinformation auf der zweiten Vorderseite der optischen Platte aufgezeichnet ist oder nicht;
    Konvergieren des durchgelassenen Lichts auf der ersten Vorderseite der optischen Platte gemäß den ersten Servosignalen in Fällen, in denen die Unterscheidungsinformation auf der zweiten Vorderseite der optischen Platte aufgezeichnet ist; und
    Reproduzieren der Aufzeichnungsinformation aus dem aus dem durchgelassenen Licht erzeugten Aufzeichnungsinformationssignal.
  61. Optische Plattenvorrichtung mit:
    einer Optikkopfvorrichtung (51, 61, 65, 67, 70, 71, 81, 91, 101, 111, 121, 151, 161) nach Anspruch 33, worin ein Informationssignal, ein Brennpunkt-Fehlersignal und ein Nachführungs-Fehlersignal als das elektrische Signal vom Photodetektor abgegeben werden;
    einem Drehmittel (178) zum Drehen eines Informationsmediums (171, 174, 25) das eines der ersten und zweiten Aufzeichnungsmedien ist;
    einem Bewegungsmittel (177) zum Bewegen der Optikkopfvorrichtung;
    einem Betätigungsmittel (58) zum Betätigen der Objektivlinse der Optikkopfvorrichtung;
    einem Brennpunktsteuermittel (57, 63, 104, 136, 143) zum Steuern des Betätigungsmittels, um eine erste Brennpunktsteuerung entsprechend dem Informationsmedium der ersten Dikke für die Optikkopfvorrichtung und eine zweite Brennpunktsteuerung entsprechend dem Informationsmedium der zweiten Dicke für die Optikkopfvorrichtung gemäß dem durch die Optikkopfvorrichtung gelesenen Brennpunkt-Fehlersignal durchzuführen;
    einem Nachführungssteuermittel (57, 63, 104, 136, 143) zum Steuern des Betätigungsmittels, um eine erste Nachführungssteuerung entsprechend dem Informationsmedium der ersten Dicke für die Optikkopfvorrichtung und eine zweite Nachführungssteuerung entsprechend dem Informationsmedium der zweiten Dicke für die Optikkopfvorrichtung gemäß dem durch die Optikkopfvorrichtung gelesenen Nachführungs-Fehlersignal durchzuführen; und
    einem Feststellungsmittel (57, 163, 104, 136, 143) zum Feststellen, ob das Informationsmedium die erste Dicke oder die zweite Dicke aufweist.
  62. Optische Plattenvorrichtung nach Anspruch 61, in der die Objektivlinse der Optikkopfvorrichtung durch das Bewegungsmittel in einer Richtung zum Informationsmedium bewegt wird und die Objektivlinse der Optikkopfvorrichtung auf dem Informationsmedium durch das Betätigungsmittel unter der Steuerung des Brennpunktsteuermittels fokussiert wird, um eine Intensität des Brennpunkt-Fehlersignals in einem Fall auf Null zu verringern, in dem die Intensität des Brennpunkt-Fehlersignals eine Schwelle übersteigt.
  63. Optische Plattenvorrichtung nach Anspruch 61 oder 62, in der das durch die Objektivlinse konvergierte durchgelassene Licht durch ein Substrat geht, der erste Brennpunkt des durchgelassenen Lichts an einer um eine erste Dicke von der Oberfläche des Substrats beabstandeten Position plaziert ist, ein Strahl eines durch die Objektivlinse konvergierten gebeugten Lichts durch das Substrat geht und der zweite Brennpunkt des Strahls eines gebeugten Lichts an einer von der Oberfläche des Substrats um eine von der ersten Dicke verschiedenen zweiten Dicke beabstandeten anderen Position plaziert ist.
EP94300717A 1993-02-01 1994-01-31 Zusammengesetzte Objetivlinse mit zwei Brennpunkten, und Vorrichtung mit dieser Linse Expired - Lifetime EP0610055B1 (de)

Priority Applications (9)

Application Number Priority Date Filing Date Title
EP05012296A EP1577887A3 (de) 1993-02-01 1994-01-31 Zusammengesetzte Objektivlinse mit zwei Brennpunkten und Vorrichtung mit dieser Linse
EP99123036A EP0992988A3 (de) 1993-02-01 1994-01-31 Optisches Plattengerät
EP03020260A EP1381039B1 (de) 1993-02-01 1994-01-31 Vorrichtung mit einer zusammengesetzten Objektivlinse mit zwei Brennpunkten
EP06021193A EP1736976B1 (de) 1993-02-01 1994-01-31 Sammelobjektiv mit zwei Brennpunkten und Vorrichtung damit
EP97122035A EP0836178B1 (de) 1993-02-01 1994-01-31 Optische Platte
EP03020259A EP1381038B1 (de) 1993-02-01 1994-01-31 Zusammengesetzte Objektivlinse mit zwei Brennpunkten und Vorrichtung mit dieser Linse
EP03020262A EP1381034B1 (de) 1993-02-01 1994-01-31 Zusammengesetzte Objektivlinse mit zwei Brennpunkten und Vorrichtung mit dieser Linse
EP00111253A EP1049084B8 (de) 1993-02-01 1994-01-31 Zusammengesetzte Objektivlinse mit zwei Brennpunkten und Vorrichtung mit dieser Linse
EP03020261A EP1376558B1 (de) 1993-02-01 1994-01-31 Zusammengesetzte Objektivlinse mit zwei Brennpunkten und Vorrichtung mit dieser Linse

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JP1443293 1993-02-01
JP1443293 1993-02-01
JP14432/93 1993-02-01
JP193353/93 1993-08-04
JP19335393 1993-08-04
JP19335393 1993-08-04

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EP97122035A Division EP0836178B1 (de) 1993-02-01 1994-01-31 Optische Platte
EP00111253A Division EP1049084B8 (de) 1993-02-01 1994-01-31 Zusammengesetzte Objektivlinse mit zwei Brennpunkten und Vorrichtung mit dieser Linse
EP99123036A Division EP0992988A3 (de) 1993-02-01 1994-01-31 Optisches Plattengerät

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EP0610055A2 EP0610055A2 (de) 1994-08-10
EP0610055A3 EP0610055A3 (de) 1995-01-11
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EP94300717A Expired - Lifetime EP0610055B1 (de) 1993-02-01 1994-01-31 Zusammengesetzte Objetivlinse mit zwei Brennpunkten, und Vorrichtung mit dieser Linse
EP00111253A Expired - Lifetime EP1049084B8 (de) 1993-02-01 1994-01-31 Zusammengesetzte Objektivlinse mit zwei Brennpunkten und Vorrichtung mit dieser Linse
EP06021193A Expired - Lifetime EP1736976B1 (de) 1993-02-01 1994-01-31 Sammelobjektiv mit zwei Brennpunkten und Vorrichtung damit
EP03020260A Expired - Lifetime EP1381039B1 (de) 1993-02-01 1994-01-31 Vorrichtung mit einer zusammengesetzten Objektivlinse mit zwei Brennpunkten
EP03020259A Expired - Lifetime EP1381038B1 (de) 1993-02-01 1994-01-31 Zusammengesetzte Objektivlinse mit zwei Brennpunkten und Vorrichtung mit dieser Linse
EP03020262A Expired - Lifetime EP1381034B1 (de) 1993-02-01 1994-01-31 Zusammengesetzte Objektivlinse mit zwei Brennpunkten und Vorrichtung mit dieser Linse
EP05012296A Withdrawn EP1577887A3 (de) 1993-02-01 1994-01-31 Zusammengesetzte Objektivlinse mit zwei Brennpunkten und Vorrichtung mit dieser Linse
EP99123036A Withdrawn EP0992988A3 (de) 1993-02-01 1994-01-31 Optisches Plattengerät
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EP06021193A Expired - Lifetime EP1736976B1 (de) 1993-02-01 1994-01-31 Sammelobjektiv mit zwei Brennpunkten und Vorrichtung damit
EP03020260A Expired - Lifetime EP1381039B1 (de) 1993-02-01 1994-01-31 Vorrichtung mit einer zusammengesetzten Objektivlinse mit zwei Brennpunkten
EP03020259A Expired - Lifetime EP1381038B1 (de) 1993-02-01 1994-01-31 Zusammengesetzte Objektivlinse mit zwei Brennpunkten und Vorrichtung mit dieser Linse
EP03020262A Expired - Lifetime EP1381034B1 (de) 1993-02-01 1994-01-31 Zusammengesetzte Objektivlinse mit zwei Brennpunkten und Vorrichtung mit dieser Linse
EP05012296A Withdrawn EP1577887A3 (de) 1993-02-01 1994-01-31 Zusammengesetzte Objektivlinse mit zwei Brennpunkten und Vorrichtung mit dieser Linse
EP99123036A Withdrawn EP0992988A3 (de) 1993-02-01 1994-01-31 Optisches Plattengerät
EP97122035A Expired - Lifetime EP0836178B1 (de) 1993-02-01 1994-01-31 Optische Platte

Country Status (4)

Country Link
US (1) US5446565A (de)
EP (10) EP1376558B1 (de)
JP (2) JP2532818B2 (de)
DE (8) DE69435325D1 (de)

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EP1381038A2 (de) 2004-01-14
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JPH0798431A (ja) 1995-04-11
EP1376558A3 (de) 2004-04-21
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DE69434045T2 (de) 2005-10-06
EP0610055A3 (de) 1995-01-11
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DE69435325D1 (de) 2010-12-30
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US5446565A (en) 1995-08-29
EP1381038A3 (de) 2004-03-31
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